Yeast vector comprising a shortened promoter sequence

ABSTRACT

An object of the present invention is to provide a vector which can be integrated into a yeast chromosome in a high number of copies. Another object of the present invention is to provide a modified vector which can be integrated into the yeast chromosome in a high number of copies and of which expression units stably maintain on the chromosome. The vector according to the present invention comprises a marker gene for selecting transformants, a shortened promoter sequence which is operably linked to the marker gene and a sequence homologous to the chromosomal DNA of  Candida utilis , and optionally a heterologous gene or a gene derived from  C. utilis , wherein the vector is linearized by cleaving within said homologous DNA sequence or at both ends of the homologous DNA sequence with restriction enzymes, and wherein the heterologous gene or the gene derived from  C. utilis  can be integrated into the chromosomal DNA of  C. utilis  by homologous recombination.

This application is a 371 of PCT/JP97/02924 filed Aug. 22, 1997.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vector which is integrated into the chromosome of yeast, specifically Candida utilis, with a high number of copies and which can be stably maintained even under nonselective culture conditions. The present invention also relates to heterologous gene expression, specifically the high-level expression of a single chain monellin and amylase, using said vector, and further relates to a method for isolating and purifying a single-chain monellin from single-chain monellin-producing recombinant yeast cells.

2. Background Art

In order to prepare gene products in large quantities using recombinant DNA procedures, it is necessary not only to select an appropriate host but also to increase the number of gene transcripts, to improve the translation efficiency, and to improve the stability of proteins produced in the various steps of gene expression. In order to increase the number of gene transcript for high-level production of gene products, it is necessary to use a highly effective transcription promoter and it is also important to increase the number of copies of the gene-expression unit which consists of the transcription promoter/terminator sequence and the gene to be expressed, thereby increasing the number of transcripts as a whole. Furthermore, for industrial scale production, it is extremely important that the gene-expression unit be stably maintained in the microbial cells. Plasmid vectors are at a disadvantage in this regard and generally stabilized by integration into a chromosome.

Regarding several yeast species other than C. utilis, it has been recently reported that dozens of copies of a vector could be integrated into the ribosomal RNA gene (rDNA) regions by using the vector carrying a transformation marker gene in which the promoter region was trancated to reduce the expression level (Lopes T. S. et al., Gene, 79, 199-206, 1989; Bergkamp R. J. M. et al., Curr. Genet., 21, 365-370, 1992; Le Dall M. T. et al., Curr. Genet., 26, 38-44, 1994).

However, it has been shown that to achieve high-copy-number integration into the chromosome, it is necessary to integrate the vector into the ribosomal RNA gene regions; otherwise, a large number of copies will not be obtained when the vector is integrated into other gene loci (Lopes T. S. etal., Gene, 105, 83-90, 1991). It has further been reported that the introduced genes might not be sustained due to recombination between their repetitive sequences because the integrated vectors existed in a tandem form in the chromosome (Lopes T. S. et al., Yeast, 12, 467-477, 1996). In particular, when microbial cells are cultured under nonselective conditions or microbial growth is slow (for example, when the expression product is present in abundance in the microbial cells), successive cultivation for generations will result in an increase in the ratio of cells without vectors. Accordingly, when recombinant yeasts are cultured under nonselective conditions (particularly in a large-scale culture), stable maintenance of the integrated vectors is of extreme importance. It has been reported that an expression unit integrated into the chromosome was stabilized by shortening the size of vector DNA (Lopes T. S. et al., Yeast, 12, 467-477, 1996).

Candida utilis, a yeast which efficiently assimilates pentoses such as xylose, has been approved to use as a food additive by the Food and Drug Administration (FDA) along with Saccharomyces cerevisiae and S. fragilis. A transformation system for Candida utilis using homologous recombination was developed recently, and heterologous protein production was reported (WO/95/32289). However, further improvements as to high-copy-number introduction of the vector into the chromosome and stabilization of the expression units are still to be achieved.

Sweet proteins are expected to be extensively used as a highly safe, low calorie sweetener, food additive, or sweetening agent in foods, drugs and the like, and even animal feed. Examples of such sweet proteins include monellin and thaumatin.

Thaumatin is a protein which can increase the palatability of food (i.e., enhance flavor and aroma) and is extracted from seed coats of the fruit of plant, Thaumatococcus daniellii Benth. However, although it is commercially available, the industrial use of plant-derived thaumatin is extremely limited because of the scarce availability of fruit for extraction. Although the production of thaumatin in a number of microbial hosts has been tried to date, published reports would indicate that expression of the protein was extremely difficult, and the protein so obtained was of minimal sweetness (Zemanek E. C. and Wasserman B. P., Critical Reviews in Food Science and Nutrition, 35, 455-466, 1995).

Monellin, a protein found in the fruit of the tropical plant Dioscoreophyllum cumminsii, is more than 2,000 times sweeter than sucrose on a weight basis, and its amino acid sequence is known. This protein comprises two nonhomologous subunits, A and B, and its tertiary structure has been reported (Hudson G. et al., Biochem. Biophys. Res. Comm., 71, 212-220,1976; Ogata C. et al., Nature, 328, 739-742, 1987; van der Wel H., FEBS Letters, 21, 88-90, 1972; Morris J. A. et al., Biochim. Biophys. Acta. 261, 114-122, 1972; Bohak Z. et al., Biochim. Biophys. Acta., 427, 153-170, 1976; Frank G. Hoppe-Seyler's Z. Physiol. Chem., 357, 585-592, 1976). Natural monellin rapidly loses its sweetness at high temperatures at acidic pHs. Attempts are under way to produce a more thermally stable protein which retains its sweetness by linking the two chains comprising monellin, namely, linking the N-terminal of the subunit A with the C-terminal of the subunit B to make a single polypeptide chain (Japanese Patent 1990/504028; Japanese Patent Laid-open 1993/70494; Kim S-H. etal., ProteinEngineering, 2, 571-575, 1989). This single-chain monellin having excellent properties is being expected for use in food as a low calorie, highly stable protein sweetener, a food additive in place of conventional sweetening agents, or a sweetening agent.

However, as long as the present inventors know, the large-scale microbial production of monellin has not been reported.

SUMMARY OF THE INVENTION

It has been shown that, when the cycloheximide-resistance L41 gene is used as a marker gene in C. utilis, the number of integrated vectors (copies) into the host by homologous recombination is generally about 3 to 10 (at most about 20). The present inventors have now found that the number of the copies increases to as much as 20 to 90 when the promoter which is operably linked to the marker gene is shortened.

It has also been known that the number of copies in yeast cells other than C. utilis could be increased only by targeting rDNA sequences for the integration. Even when rDNA sequences is targeted for the integration, the expression units are inevitably excised. The present inventors have now found that, in addition to shortening the promoter linked to the marker gene, targeting of the sequence homologous to the chromosomal DNA at gene loci other than rDNA sequences would not only further increase the number of the copies (exceeding the number achieved with rDNA target sequences), but would also stabilize the expression units on the chromosome.

The present inventors have also found that proteins (in particular, single-chain monellin and amylase) can be expressed abundantly by using the vector and that when the extract obtained from single-chain monellin-producing cells is treated with heat and/or acid, monellin remains in solution while most undesirable proteins derived from the yeast will precipitate.

The present inventors have further found that the frequency of usage of codons in the amylase gene (derived from the thermophilic bacteria Sulfolobales solfataricus) for expression in C. utilis differs markedly from that in the structural gene of glyceraldehyde-3-phosphate dehydrogenase (GAP), which is one of the proteins best expressed in C. utilis. Moreover, modification of the amylase gene sequence markedly increases the level of amylase expression. The present invention is based on these findings.

Accordingly, an object of the present invention is to provide a vector which can be integrated in a high number of copies into the yeast chromosome. Another object of the present invention is to provide a modified vector which can be integrated in a high number of copies into a yeast chromosome and of which expression units maintain stably on the chromosome.

Another object of the present invention is to provide a method for transformation using said vector, a host transformed by said vector, a method of producing proteins by culturing said host, and a method of purifying the single-chain monellin.

Furthermore, another object of the present invention is to provide a shortened promoter to improve the number and stability of the vector to be integrated, and an amylase gene modified to be highly expressed in C. utilis.

The vector according to the present invention is a vector which comprises a marker gene for selecting transformants, a shortened promoter sequence which is operably linked to the marker gene and a sequence homologous to the chromosomal DNA of C. utilis (“homologous DNA sequence”), and optionally a heterologous gene or a gene derived from C. utilis, wherein the vector is linearized by cleaving within said homologous DNA sequence or at both ends of the homologous DNA sequence with restriction enzymes, and wherein the heterologous gene or the gene derived from C. utilis can be integrated into the chromosomal DNA of C. utilis by homologous recombination.

The vector according to the present invention is a vector which comprises a gene conferring cycloheximide-resistance, a heterologous gene or a gene derived from C. utilis, and optionally a promoter sequence and a terminator sequence which are operably linked to the heterologous gene or the gene derived from C. utilis, wherein the heterologous gene or the gene derived from C. utilis, and optionally the DNA sequence containing the promoter and the terminator are flanked at both ends by the gene conferring cycloheximide-resistance, and wherein the vector is linearized by cleaving within the gene sequence conferring cycloheximide resistance or at both ends of said gene sequence with restriction enzymes, and the heterologous gene or the gene derived from C. utiliscan be integrated into the chromosomal DNA of C. utilis by homologous recombination.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows restriction enzyme cleavage maps of plasmids containing ribosomal DNAs.

FIG. 2 shows the structures of ribosomal DNAs, the strategy for DNA sequence determination, and the structures of subcloned plasmids. FIG. 2 (a) shows structures of plasmids pCRE1, pCRE2, pCRE3, pCRX1, pCRX2, pCRX3, and pCRX4, and FIG. 2 (b) shows the restriction enzyme cleavage map of an approximately 13.5 kb DNA fragment containing ribosomal DNAs of C. utilis.

FIG. 3 shows restriction enzyme cleavage maps of plasmids containing the URA3 gene and the complementing activity of these plasmids with S. cerevisiae ura3⁻ mutation.

FIG. 4 shows the strategy for determination of DNA sequence of the URA3 gene and the restriction enzyme cleavage map.

FIG. 5 shows the sequence (SEQ ID NO:34) of a DNA fragment containing the URA3 gene.

FIG. 6 shows the amino acid sequence (SEQ ID NO:36) deduced from the DNA sequence of the URA3 gene and the sequence (SEQ ID NO:35) of the DNA encoding for the amino acid sequence.

FIG. 7 shows the amino acid sequence (SEQ ID NO:36) deduced from the DNA sequence of the URA3 gene and the sequence (SEQ ID NO:35) of the DNA encoding for the amino acid sequence (continued from FIG. 6).

FIG. 8 shows restriction enzyme cleavage maps of the plasmids containing the L41 gene and the strategy for DNA sequence determination.

FIG. 9 shows the sequence (SEQ ID NO:37) of a DNA fragment containing the L41 gene.

FIG. 10 shows the amino acid sequence (SEQ ID NO:39) deduced from the DNA sequence of the L41 gene and the sequence (SEQ ID NO:38) of DNA coding for the amino acid sequence.

FIG. 11 shows the construction of plasmids PCLBS10 and pCLBS12.

FIG. 12 shows the structure of plasmids pCLRE2, pCLRE3, pCLRX1 and pCLRX2.

FIGS. 13a and 13 b, shows the structure of plasmid pCLRE2. FIG. 13b shows locations of the 5′ terminal in the cycloheximide-resistance L41 gene promoter (SEQ ID NO:40) of plasmids pCLRE11, pCLRE15, pCLRE16, pCLRE17, pCLRE18, and pCLRE19.

FIG. 14 shows results of Southern blot analysis of transformants with plasmids pCLRE11, pCLRE15, pCLRE16 and pCLRE17 (photographs of electrophoresis) and the number of copies of integrated vectors.

FIG. 15 shows the construction of plasmids pCLR215, pCLR216 and pCLR217.

FIG. 16 shows the construction of plasmids pCRAL10 and pCRAL11.

FIG. 17 shows the construction of plasmids pURAL10 and pURAL11.

FIG. 18 shows the construction of plasmid pCL12.

FIG. 19 shows the restriction enzyme cleavage map of a plasmid containing the glyceraldehyde-3-phosphate dehydrogenase (GAP) gene, the strategy for DNA sequence determination, and a method for obtaining a promoter fragment and a terminator fragment by PCR.

FIG. 20 shows the construction of plasmids pCLRM215, pCLRM216, pCLRM217, pRM10, pRM11, pUM10, and pUM11.

FIG. 21 (1) is a photograph showing results of the analysis of solubleproteins of C. utilis transformantswithplasmidspCLRE4, pCLRM216, pRM11, and pUM11 using SDS-polyacrylamide gel electrophoresis.

FIG. 21 (2) is a photograph showing results of the analysis of soluble proteins of S. cerevisiae transformants with plasmid pCTMNY1 using SDS-PAGE.

FIG. 22 is a photograph showing results of the analysis of soluble proteins of C. utilis transformants with plasmids pCLRM216, pRM11, and pUM11 after 50 generations of growth, using SDS-polyacrylamide gel electrophoresis.

FIG. 23 is a photograph showing results of the analysis of samples of soluble proteins prepared from C. utilis transformants with plasmid pRM11, which were heat-treated or acid-treated, or purified by column chromatography, using SDS-polyacrylamide gel electrophoresis.

FIG. 24 shows primers used in the synthesis of segments A-1 (SEQ ID NO:41-49) and A-2 (SEQ ID NO:45-48) of the modified amylase gene.

FIG. 25 shows primers used in the synthesis of segments A-3 (SEQ ID NO:49-52) and A-4 (SEQ ID NO:45-48) of the modified amylase gene.

FIG. 26 shows primers used in the synthesis of segments A-5 (SEQ ID NOS:57-58), A-6 (SEQ ID NOS:59-62) and A-7 (SEQ ID NOS:63-66) of the modified amylase gene.

FIG. 27 shows the construction of plasmids pCRAL11UA, pURAL11UA, and pCL12UA.

FIG. 28 is a photograph showing results of the analysis of soluble proteins of C. utilis transformants with plasmids pCLRE4 and pURAL11UA, using SDS-PAGE. +: Heat-treated sample; −: non-heated sample.

FIG. 29 shows the construction of plasmid pRALGIF2.

DETAILED DESCRIPTION OF THE INVENTION

Shortened Promoter

The term “shortened promoter” as used herein refers to a promoter trancated at its 5′ side, which decreases the transformation frequency of the vector by decreasing the level of expression of the marker gene but increases the number of copies of the vector in the host cells.

As shown in the Examples, a vector having a marker gene to be expressed by a promoter shortened by trancating its 5′-end region is characterized in that its transformation frequency is reduced by decreasing the level of expression of the marker gene but is present in a higher copy number in the transformed host cells, as compared to a vector ligated with a marker gene to be expressed by a promoter of normal length.

The shortened promoter in the present invention can be selected from those which can be operably linked to a marker gene usable in C. utilis.

Examples of such promoters include those derived from the L41 gene of C. utilis, the phosphoglycerate acid kinase (PGK) gene, the glyceraldehyde-3-phosphoric acid hydrogenase (GAP) gene, and the plasma membrane proton ATPase (PMA) gene.

When the promoter is obtained from the L41 gene, the shortened promoter sequence contains the DNA sequence X to 192 of SEQ ID NO. 1. X herein refers to an integer from 1 to 111. The DNA sequences of SEQ ID NO. 2 and NO. 3 are those obtained by trancating the 5′ end sequence of the DNA sequence of SEQ ID NO. 1.

The shortened promoter derived from the L41 gene is a novel DNA sequence. Accordingly, another aspect of the present invention provides the DNA sequence X to 192 (wherein X represents an integer from 1 to 111) of SEQ ID NO. 1 and the DNA sequences of SEQ ID NO.2 and NO. 3. These sequences are useful as the promoter sequence for a selective marker gene of vectors for chromosomal integration.

In the present invention, the shortened promoter is operably linked to the marker gene. In certain cases, a terminator sequence may be added downstream of the marker gene.

Homologous DNA Sequence

The vector according to the present invention has a homologous DNA sequence for homologous recombination into a host chromosome.

Examples of such homologous DNA sequences in the present invention include the rDNA (ribosomal DNA) sequence, the URA3 gene sequence, the L41 gene sequence, the PGK gene sequence, the GAP gene sequence, the PMA gene sequence, and partial DNA sequences thereof. A sequence derived from the chromosome of C. utilis is preferable. Genes from C. utilis other than the genes described above can similarly be used. A heterologous gene can be integrated at any site on the chromosome depending on a function of the sequence being used. The term “rDNA sequence” as used herein also refers to a series of rRNA genes.

According to the present invention, a gene sequence other than the rDNA sequence from C. utilis is preferably used as a homologous DNA sequence. It is advantageous to use a gene sequence other than the rDNA sequence because it not only increases the number of vector copies but also remarkably improves the stability of the vector on the chromosome. Examples of such a sequence include the URA3 gene sequence, the L41 gene sequence, the PGK gene sequence, the GAP gene sequence, and the PMA gene sequence derived from C. utilis, and partial DNA sequences thereof. Genes other than the rDNA sequence from C. utilis can also be used.

This vector is linearized for use by digestion at an appropriate restriction enzyme cleavage site in a homologous DNA sequence in the vector (plasmid DNA). This enables a plasmid DNA fragment to be integrated into the C. utilis chromosome by homologous recombination.

In a preferred embodiment of the present invention, within a vector, a DNA sequence comprising a marker gene and a heterologous gene is flanked at both ends by the homologous DNA sequence described above. According to this embodiment, the homologous DNA sequence of the vector DNA is cleaved at both ends by restriction enzymes to obtain a DNA fragment containing the marker gene and the heterologous gene having the homologous DNA sequence at both ends. The DNA fragment thus obtained can also be integrated into the C. utilis chromosomal DNA by homologous recombination. It is advantageous from a safety point of view to use a vector which is linearized in this manner by cleaving at the restriction enzyme cleavage sites corresponding to both ends of the homologous sequence because no DNA derived from the plasmid is integrated into the chromosome (namely, there is no possibility to produce unknown gene products derived from bacteria).

The expression “a DNA fragment (or sequence) is integrated in the C. utilis chromosome by homologous recombination” as used herein means that as long as the DNA fragment is integrated into the C. utilis chromosome, its actual mode of integration is not restricted, but at least, the following modes are included:

(1) Homologous recombination occurs between the DNA sequence of the C. utilis chromosome and the homologous DNA sequence at both ends of the DNA fragment and the DNA fragment is “inserted” at the cleaved site.

(2) Homologous recombination occurs between the DNA sequence of the C. utilis chromosome and the homologous DNA sequence at both ends of the DNA fragment such that the vector DNA fragment is “substituted” with a part of the C. utilis chromosome.

In mode (2), stability of the integrated DNA fragment in the chromosome is further improved because no repetitive sequence of the target sequence is formed before or after the inserted DNA fragment.

Marker Gene

According to the present invention, the marker gene can be a drug-resistance gene. Examples of drug resistance genes include those which can select C. utilis transformants, such as a gene conferring cycloheximide resistance (e.g., the modified cycloheximide-resistance L41 gene), a gene conferring antibiotic G418 resistance (e.g., the aminoglycoside-3′-phosphotransferase (APT) gene derived from bacterial transposon Tn903), a gene conferring hygromycin B resistance (e.g., the hygromycin B phosphotransferase (HPT) gene derived from an E. coli plasmid).

The L41 gene codes for the ribosomal protein L41 which is sensitive to cycloheximide. The modified cycloheximide-resistance L41 gene is a gene in which Pro at position 56 of the amino acid sequence of L41 is substituted with Gln. L41 cycloheximide resistance is conferred by this substitution (WO/95/32289).

In addition to the G418-resistance gene and hygromycin B phosphotransferase gene, examples of drug resistance genes derived from bacteria which can be used as a selective marker for transformants include antibiotic-resistance genes, such as the chloramphenicol acetyl transferase gene (chloramphenicol resistance) (Hadfield, C. et al., Gene, 45, 149-158, 1986), the blasticidin deaminase gene (blasticidin resistance) (Izumi, M. et al., Exp. Cell Res., 197, 229-233, 1991), and the phleomycin-resistance gene (Wenzel, T. J. et al., Yeast, 8, 667-668, 1992). Other usable known drug-resistance genes are the dehydrofolate reductase gene (methotrexate resistance) (Miyajima, A. et al., Mol. Cell Biol., 4, 407-414, 1984), sulfometuronmethyl-resistance gene, adominantgenederivedfromyeast (Casey, G. P. etal., J. Inst. Brew., 94, 93-97, 1988), the CUP1 gene (copper resistance) (Henderson, R. C. A. et al., Current Genet., 9, 133-138, 1985), and the CYH2 gene (cycloheximide resistance) (Delgado, M. et al., EBC Congress, 23, 281-288, 1991).

Heterologous Genes and Genes Derived from C. utilis

According to one embodiment of the present invention, a heterologous gene or a gene derived from C. utilis (“structural gene”) is ligated into the vector according to the present invention to construct a vector carrying the structural gene. These structural genes can be stably integrated into the C. utilis chromosome by transforming C. utilis using this vector. The protein encoded by a structural gene can be produced using C. utilis by culturing a transformant thus obtained in an appropriate medium, isolating the expressed product of the structural gene from the culture, and purifying it by a method appropriate for the expressed product. A method for expressing the structural gene in C. utilis is provided. The term “heterologous gene” as used herein refers to a gene which does not exist in the host C. utilis chromosome, or a partial DNA thereof.

The structural gene is preferably combined with a regulatory region which independently controls the expression of the gene, or it can be expressed under a regulatory region of the gene itself which is disrupted during transformation. Such sequences are needed to function in C. utilis and preferable examples of such sequences include the promoter sequences and the terminator sequences of the PGK gene, GAP gene, and the PMA gene according to the present invention as mentioned after.

As shown in Examples, heterologous genes such as the single-chain monellin gene, the GIF gene and the amylase gene were successfully expressed using the promoter sequence and the terminator sequence of the GAP gene, in accordance with the present invention.

Furthermore, it will be appreciated by those skilled in the art that structural genes (for example, genes coding for albumin, α- or β-globulin, factor VIII, factor IX, fibronectin, α-1-antitrypsin, interleukin, interferon, G-CSF, GM-CSF, PDGF, EGF, FGF, erythropoietin, thrombopoietin, insulin, antigen polypeptides derived from viruses for vaccine production, proteins having immune suppression activity (e.g., glycosylation inhibiting factor (GIF)), chymosin, amylase, lipase, cellulase, protease and pectinase) can be expressed using the promoter and terminator sequences of the phosphoglycerate kinase gene, the promoter and terminator sequences of the glyceraldehyde-3-phosphate dehydrogenase gene, or the promoter and terminator sequences of the plasma membrane proton ATPase gene. It will also be appreciated by those skilled in the art that characteristics of C. utilis can be modified by expressing structural genes in C. utilis.

Heterologous genes or genes derived from C. utilis can be modified to be highly expressed in C. utilis. The gene can be modified to enable high level expression in C. utilis by optimizing the gene sequence to correlate with those codons most frequently used in C. utilis. For example, the gene sequence can be optimized according to the codons used with genes which are highly expressed in C. utilis.

A modified gene is synthesized by altering bases in codons without changing the amino acid sequence which the gene encodes. Specifically, those codons coding for the 18 amino acids, other than methionine and tryptophan, which are most frequently found in highly expressed genes such as the glyceraldehyde-3-phosphate-dehydrogenase (GAP) gene derived from C. utilis are used. It is desirable to design the structural gene in such a manner that appropriate restriction enzyme cleavage sites are located at intervals of about 250 to 300 bp so that the gene can be synthesized as several partitioned segments.

For example, the synthesized gene can be constructed as follows:

A DNA sequence is designed in such a manner that appropriate restriction enzyme cleavage sites are located in the structural gene at intervals of about 180 to 320 bp so that the structural gene synthesized as several partitioned segments can be ligated utilizing the restriction enzyme cleavage sites. Using the DNA sequence designed for the gene, a pair of single-stranded oligonucleotides having about 50 to 100 bases are synthesized by the conventional method and then a double-stranded segment is synthesized by PCR using these fragments as templates. Specifically, in synthesizing a 180-bp double-stranded DNA, a pair of 100 base oligonucleotides, which are overlapped about 20 bp at their 3′ ends, are synthesized. The targeted double-stranded DNA is then obtained by a PCR reaction using these oligonucleotides as templates under the standard conditions. To synthesize a double-stranded DNA of about 340 bp, a second PCR reaction is carried out using as templates the double-stranded DNA obtained as described above and a pair of oligonucleotides of 100 bases, which are synthesized to have overlapped sequences of about 20 bp with the double-stranded DNA at their 3′ ends. This final synthesized double-stranded DNA is designed to have specific restriction enzyme cleavage sites at both ends and preferably to have additional sequences of some 2 nucleotides outside of the restriction enzyme cleavage sites of both ends to facilitate digestion by the restriction enzymes.

One example of a modified heterologous gene is the amylase gene of SEQ ID NO. 14. The DNA sequence of SEQ ID NO. 14 is anovel sequence. Accordingly, another aspect of the present invention provides the amylase gene consisting of the DNA sequence of SEQ ID NO. 14. This amylase gene can be highly expressed in yeast such as C. utilis (see Examples).

Furthermore, the vector according to the present invention can be used for transformation of cells other than C. utilis. It is preferable to select an appropriate DNA fragment for transformation when cells other than C. utilis are used as host cells. Examples of such DNA fragments for E. coli include bacterial plasmid DNAs such as pbluescript and pUC19. For yeast of family Saccharomyces, yeast-E. Coli shuttle vectors such as YEp13 and YCp50 (Methods in Enzymology, 194, 195-230, Academic Press, 1991) can be used.

A preferable embodiment of the vector according to the present invention is a vector which comprises a marker gene conferring cycloheximide resistance, a shortened promoter comprising the DNA sequence X-192 (wherein X represents an integer from 1 to 111) of SEQ ID NO. 1 operably linked to the marker gene, a sequence homologous to the chromosomal DNA of C. utilis other than the rDNA sequence (“homologous DNA sequence”), and a heterologous gene (e.g., the single-chain monellin gene, the amylase gene, or the glycosylation inhibiting protein gene, which may be modified to be highly expressed in C. utilis) or a gene derived from C. utilis, and optionally a promoter sequence and a terminator sequence derived from C. utilis which are operably linked to the heterologous gene or the gene derived from C. utilis, wherein the vector is linearized by cleaving within or at both ends of the homologous DNA sequence with restriction enzymes, and wherein the heterologous gene or the gene derived from C. utilis can be integrated into the chromosomal DNA of C. utilis by homologous recombination.

More preferably, the DNA sequence containing a marker gene, a shortened promoter, a heterologous gene or a gene derived from C. utilis, and optionally a promoter and a terminator, is flanked by the URA3 gene at both ends.

The homologous DNA sequence can preferably be the URA3 gene sequence or a partial DNA sequence thereof.

Another aspect of the present invention provides a vector which comprises a gene conferring cycloheximide resistance, a heterologous gene or a gene derived from C. utilis, and optionally a promoter sequence and a terminator sequence derived from C. utilis which are operably linked to the heterologous gene or the gene derived from C. utilis, and wherein the vector is linearized by cleaving within or at both ends of the gene sequence conferring cycloheximide resistance by restriction enzymes, and wherein the heterologous gene or the gene derived from C. utilis can be integrated into the chromosomal DNA of C. utilis by homologous recombination.

The DNA sequence containing the heterologous gene or the gene derived from C. utilis, and optionally the promoter and the terminator, is flanked by the 5′ end part and the 3′ end part of the gene conferring cycloheximide resistance. When such vectors are integrated into the chromosomal DNA of C. utilis in a tandem form, the gene conferring cycloheximide resistance divided into the 5′ end part and the 3′ end part becomes united on the chromosome. As a result, transformants regain cycloheximide resistance and can be selected on a selective medium. The gene conferring cycloheximide resistance in the vector functions not only as a “homologous DNA sequence” for integration into the chromosome but also as a marker gene to select the transformants.

The term “vector” as used herein includes plasmids derived from bacteria.

Transformation

Transformants according to the present invention can be obtained by introducing a vector DNA (plasmid DNA) into a host such as C. utilis and selecting transformants which have become drug resistant.

Host cells are treated to enable them to incorporate foreign DNAs by methods conventionally used for transformation of C. utilis, such as the electric pulse method, the protoplast method, the lithium acetate method, and modified methods thereof.

In the electric pulse method, cells cultured up to the logarithmic growth phase are washed and then suspended in 1 M sorbitol. Pulsing can be performed under the conditions which would yield a time constant (time required to lower the voltage to about 37% of the maximum value) of about 10 to 20 milliseconds and cell viability of about 10 to 40% after pulsing. For example, the time constant and cell viability can be attained and about 500 to 1,400 transformants per 1 μg of DNA can be obtained at a capacitance of 25 μF, a resistance of 600 to 1,000 ohms, and a voltage of 3.75 to 5 KV/cm.

Furthermore, it is preferable to add a YPD medium containing 1 M sorbitol to the cell suspension after pulsing, and then incubate the suspension at 30° C. with shaking. There were occasions when no colony appeared on the selective medium plate containing cycloheximide when the cells were plated without this cultivation. An appropriate incubation time is about 4 to 6 hours; further extended incubation results in significant growth of transformants. It is also preferable to improve the transformation frequency of the transformation system according to the present invention; for example, by the addition of a carrier DNA such as salmon sperm DNA upon the contact of DNA with the cells, or by the addition of polyethylene glycol.

The lithium acetate method (Ito et al., J. Bacteriol., 153, 163-168, 1983) is extensively used for transformation of yeast of genus Saccharomyces because of its simplicity and convenience and various improved methods are reported. It has been confirmed that C. utilis can also be transformed using these methods (WO/95/32289). In particular, C. utilis can be transformed by the modified lithium method in which ethanol is added (Soni et al., Current Genet., 24, 455-459, 1993). It is also possible to increase transformation frequency by using the optimum conditions for C. utilis transformation, which can be determined experimentally by altering various conditions for the transformation; for example, cell density at cell harvest, lithium concentration, kind and concentration of polyethylene glycol, or the kind, form and amount of carrier DNA.

Examples of the host to be transformed with the vector according to the present invention include yeasts such as C. utilis. Examples of C. utilis strains include ATCC9256 (IFO 0626), ATCC9226 (IFO 1086), ATCC9950 (IFO 0988), IFO 0396, IFO 0619, IFO 0639, and KP-2059P.

All of the strains described above have been confirmed to produce transformants and express heterologous genes although three strains, ATCC9256, ATCC9226 and ATCC9950, show chromosomal polymorphism (Stoltenburg et al., Curr. Genet., 22, 441-446, 1992) (WO/95/32289). From these observations, it will be appreciated by those skilled in the art that the vector according to the present invention can be universally used with C. utilis.

Method of Producing Proteins

According to another embodiment of the present invention C. utilis cells transformed with the vector according to the present invention are cultured and the expression product of a structural gene is isolated from the culture and purified to obtain a protein.

In a further embodiment of the present invention, the target protein can be prepared by culturing C. utilis cells transformed with the vector according to the present invention which carries the single-chain monellin gene or the amylase gene as a heterologous gene and isolating and purifying single-chain monellin or amylase from the culture. These genes may be modified to be highly expressed in the host cells.

When the rDNA was used as the target sequence, the vector alone was stable. However, the expression level decreased after 50 generations of cultivation because of a high level expression of protein. On the other hand, host cells having vectors which use sequences other than rDNA, such as the URA3 gene or the L41 gene, as the integration target stably maintained the vectors and the expression level remained high even after about 50 generations of cultivation (see Examples).

It was shown that the use of a vector which used the URA3 gene or the L41 gene as the integration target not only increased the number of copies but also remarkably improved the stability of the gene integrated into the chromosome.

The single-chain monellin, which is successfully expressed at a high level in the present invention, was proven to have a sweetness equivalent to natural monellin and a remarkably improved thermal stability in a low pH range (Japanese Patent Laid-open 1993/70494). In this molecule, chain A and chain B of natural monellin are connected by a glycine residue. The single-chain monellin primarily consists of a single chain in which subunit B of natural monellin is connected via its C terminal to the N terminal of subunit A of natural monellin by a covalent bond linker. Specifically, the single-chain monellin contains the amino acid sequence of SEQ ID NO. 6.

It is well known that the properties of proteins are virtually conserved even when their structural amino acids are partially deletedorsubstitutedorotheraminoacidsareadded. Thisfacthas also been confirmed with the single-chain monellin (Japanese Patent Publication 1990/504028, Japanese Patent Laid-open 1993/70494).

Accordingly, the term “single-chain monellin” as used herein includes monellin which has an amino acid sequence substantially substantially equivalent to that of the single-chain monellin molecule. The term “substantially equivalent amino acid sequence” refers to a peptide which has a sweetness equivalent to natural monellin even if substitution, deletion or addition of amino acids occurs. Therefore, for example, an amino acid sequence in which Glu at position 50 and Asn at position 51 of SEQ ID NO. 6 are substituted with Asn and Glu, respectively (the amino acid sequence of SEQ ID NO. 5) is called a “substantially equivalent amino acid sequence,” and a protein containing this sequence is called a “single-chain monellin.” Further, the terms “peptide” and “protein” as used herein mean the same.

Once an amino acid sequence of a protein is given, a DNA sequence coding for the amino acid sequence can be readily determined and one can select it from a variety of possible DNA sequences. Accordingly, the term “single-chain monellin gene” refers to those DNA sequences encoding the amino acid sequence of the single-chain monellin (including substantially equivalent amino acid sequences) which have degenerate codons in the sequence, in addition to the DNA sequence of SEQ ID NO. 4 and the DNA sequence coding for the amino acid sequence of SEQ ID NO. 6.

It will be appreciated by those skilled in the art that the use of those amino acid codons most suitable to the applicable yeast within the DNA sequence coding for the single-chain monellin will further improve the expression level.

The single-chain monellin which is expressed as a soluble protein in cells of yeast, including C. utilis, can be easily purified by heat treatment or acid treatment.

The heat treatment can be carried out at 50 to 70° C., preferably at about 60° C. to efficiently precipitate other undesirable proteins. The acid treatment can be carried out below pH 5, preferably at pH 4 to 5 to efficiently precipitate other undesirable proteins. Either of these treatments can increase the purity of the monellin to more than 80%.

Furthermore, the purity of the monellin can be increased to almost 100% by combining the heat treatment and acid treatment. The order of the treatments is not particularly restricted.

Furthermore, it will be appreciated by those skilled in the art that known purification procedures such as cation exchange chromatography can be used alone or in combination with the treatments described above.

Furthermore, it is preferable to make the protein concentration of the extract less than 10 mg/ml (preferably less than 3 mg/ml) to prevent coprecipitation of the single-chain onellin.

The soluble protein fraction is extracted and subjected to heat treatment or acid treatment or a combination of these treatments. The crude monellin thus obtained can be used as food or animal feed without further purification. Furthermore, monellin can be provided in combination with yeast, which is by itself an excellent food rich in various vitamins and dietary fibers, simply by an appropriate heat treatment of disrupted cells.

The methods can save time and costs for the protein purification process, which is particularly advantageous when the protein is to be used for animal feed.

EXAMPLES

The present invention is further specifically described with reference to the following examples, but it is not limited to the examples.

In this disclosure, restriction enzyme sites in the restriction enzyme maps of genes are represented by the following. Af;AflII, Ap; ApaI, Asp;Asp718, B; BamHI, Bg; BglII, C; ClaI, E; EcoRI, RV; EcoRV, H; HindIII, Hp; HpaI, K; KpnI, P; PstI, Pv; PvuII, S; SalI, Se; SpeI, Sm; SmaI, Sc; SacI, ScII; SacII, Sp; SphI, X; XbaI, and Xh; XhoI.

The methods used in the following examples are as follows:

Example 1 Preparation of Candida utilis Chromosomal DNA

The extraction of Candida utilis chromosomal DNA was carried out by the following procedure. ATCC 9950 strain of Candida utilis was inoculated in 30 ml of YPD medium and cultured at 30° C. early stationary phase. The cells were collected by centrifugation, washed with sterilized water, and collected again by centrifugation. After the cells were suspended in 3 ml of Zymolyase buffer (0.9 M sorbitol, 0.1 M EDTA, 50 mM DTT, pH 7.5), 200 μl of 0.9 M sorbitol containing 25 mg/ml Zymolyase 100T was added, and the mixture was incubated at 37° C. under shaking. After the formation of protoplast was confirmed by microscopic observation, the protoplasts were collected by centrifugation. After 3 ml of lysis buffer (50 mM Tris-HC1, 50 mM EDTA, pH 8.0) was added and the protoplasts were suspended gently and sufficiently in the buffer, 0.3 ml of 10% SDS was added, and the mixture was incubated at 65° C. overnight. Then, 1 ml of a 5 M potassium acetate solution was added, and the mixture was left standing on ice for 1 hour. Precipitates were then removed by centrifugation, 4 ml of cold ethanol was added, and the mixture was centrifuged to precipitate DNA. The precipitate was washed with 50% ethanol, dried, dissolved in 3 ml of an RNase A buffer(10 mMTris-HCl, 1 mM EDTA, 50 μg/ml RNase A, pH 7.5), and incubated at 37° C. for 30 minutes. Finally, 3 ml of 2-propanol was added and the mixture was centrifuged to remove the supernatant. Precipitates thus obtained were washed with 50% 2-propanol and dried. The precipitate was dissolved in 0.5 ml of a TE buffer and used as a Candida utilis chromosomal DNA sample.

After the partial digestion of the Candida utilis chromosomal DNA with a restriction enzyme Sau3AI, the digested mixture was layered on a 10-50% sucrose density gradient containing 0.8 M NaCl, 20 mM Tris-HCl, 10 mM EDTA (pH 8.0), and centrifuged under 120,000×g for 14 hours to fractionate the DNA fragments. Among these fragments, 10-20 kb chromosomal DNA fragment was ligated overnight with dephosphorylated λ-phage vector DASHTMII (Stratagene Cloning Systems) which had been digested with BamHI, and then subjected to in vitro packaging to construct a Candida utilis genomic DNA library.

Example 2 Isolation of the rDNA

A 400 ng portion of 5-10 kb Sau3AI partially digested DNA fragments of Candida utilis ATCC 9950 genomic DNA obtained by the sucrose density gradient centrifugation described in Example 1, and 200 ng of vector plasmid pBR322 digested with BamHI and dephosphorylated were ligated overnight with T4 DNA ligase. E. coli DH5 was transformed with this DNA solution to construct a Candida utilis genomic DNA library.

Filters were prepared for about 10,000 colonies according to the method described in Molecular Cloning, 2nd edition, Sambrook et al., p12, 21-23, Cold Spring Harbor Laboratory (1989), and screened with the 1.8 kb ³²P-labelled HindIII—EcoRI fragment containing S. cerevisiae 18S rRNA gene as a probe. The rDNA fragment used as the probe was prepared from a plasmid obtained from a genomic DNA library of Saccharomyces cerevisiae S288C [α, suc2, mal, gal2, CUP1] with a³²P-labelled oligomer corresponding to the fragment of nucleotides 4-32 at 5′-terminal of the 5.8S rRNA gene as a probe (Sone et al., Japanese Patent Publication No. 14865/1994).

Over 200 positive clones were obtained. Restriction enzyme maps of plasmids from seven clones, pCR1, pCR4, pCR5, pCR6, pCR7, pCR8 and pCR9 were constructed and aligned for comparison. The restriction enzyme maps at the both terminals were accorded (FIG. 1). It has been found from this fact that the region containing the rRNA gene of Candida utilis has an about 13 kb repetitive structure.

From these plasmids, fragments cut out by digestion with EcoRI or XbaI were subcloned into pBluescript SK- to construct plasmids pCRE1, pCRE2, pCRE3, pCRX1, pCRX2, pCRX3 and pCRX4 (FIG. 2(a)). Furthermore, these plasmids were digested with a variety of restriction enzymes and recyclized to construct a variety of deletion plasmids. DNA sequences were determined on the insertion fragments of these plasmids and the regions where the DNA sequence was determined are shown by arrows in the figure. The analysis of the DNA sequences revealed the presence of the regions which have high homology with the 18S, 5.8S and 25S rRNA genes. Thus, the location and transcriptional direction of the three rRNA genes were determined (FIG. 2(b)).

Example 3 Isolation of the Orotidine 5′-Phosphate Decarboxylase Gene (URA3 gene)

A 100 ng portion of 5-10 kb Sau3AI partially digested DNA fragments of Candida utilis ATCC 9950 genomic DNA obtained by the sucrose density gradient centrifugation described in Example 1, and 100 ng of vector plasmid YEp13 (Methods in Enzymol., 194, 195-230, 1991) digested with BamHI and dephosphorylated were ligated overnight with T4 DNA ligase. E. coli DH5 was transformed with this DNA solution to construct a genomic DNA library. After the plasmid mixture was extracted from the transformants, Saccharomyces cerevisiae YPH 500 (α his3, trp1, leu2, ade2, lys2, ura3) (Stratagene Cloning Systems) which is a ura3-strain was transformed with the plasmid DNA mixture and the transformants which did not require uracil for growth were selected on a minimal medium. Transformation of S. cerevisiae was conducted according to the lithium method described in Methods in Yeast Genetics—A Laboratory Course Manual—Rose M. D. et al., p. 122-123, Cold Spring Harbor Laboratory Press, NY (1990).

Five Ura⁺ strains were obtained from 10 μg of DNA by this procedure. Plasmid DNA was prepared from each of these transformants according to the method described in Methods in Yeast Genetics—A Laboratory Course Manual—Rose M. D. et al., p. 130, Cold Spring Harbor Laboratory Press, NY (1990). E. coli was transformed with the DNA, and a plasmid DNA was prepared. Restriction enzyme maps were constructed on the plasmids pCURA3-3 containing a 6.1 kb insert and pCURA3-5 containing a 8.1 kb insert at the BamHI site of YEp13, respectively.

Example 4 Characterization of URA3 Gene Region and Determination of DNA Sequence

In order to characterize the URA3 gene region, a 5 kb EcoRI fragment containing a region common to the plasmids pCURA3-3 and pCURA3-5 was cut out from a plasmid pCURA3-5 and ligated to the EcoRI site of a plasmid pRS314 (Stratagene Cloning Systems) to prepare a plasmid pURAE1 (FIG. 3). The YPH 500 strain was transformed with the plasmid by the lithium method. As a result, URA⁺ transformants were obtained in high frequency. This indicates that URA3 gene is present in the 5 kb EcoRI fragment, and one copy of the gene can complement the ura3⁻ mutation of Saccharomyces cerevisiae.

The plasmid pURAE1 was then digested with XhoI or PstI and recyclized by the T4 ligase reaction to give plasmids pURAE1ΔXho and pURAE1 Pst.

Furthermore, the 3.5 kb EcoRI-ClaI fragment and the 2.3 kb HindIII fragment cut out from the plasmid pURAE1 were inserted between EcoRI and ClaI sites, or at the HindIII site of the pRS314, respectively, to prepare plasmids pURAEC1 and pURAH1 (FIG. 3).

The YPH500 strain was transformed with five plasmids described above by the lithium method to examine the complementarity of ura3⁻ mutation and thus to examine whether these fragments contain the URA3 gene or not. The result is shown in FIG. 3. The results showed that the URA3 gene is located in 2.3 kb region between the EcoRI and HindIII.

Furthermore, the 2.3kb HindIII fragment containing the URA3 gene was ligated to the HindIII site of the plasmid pBluescrip SK- to prepare a plasmid pURAH2. By the deletion mutation with ExoIII nuclease and mung bean nuclease from both ends of the inserted fragment, plasmids having deletion mutation were prepared, and the DNA sequence was determined. The restriction enzyme map which has been clarified by the DNA sequence and the sequence strategy are shown in FIG. 4. The 2330 bp DNA sequence thus obtained is shown in FIG. 5, and the deduced amino acid sequence of the polypeptide consisting of 267 amino acid residues is shown in FIGS. 6 and 7.

The amino acid sequence of the polypeptide was compared with that of the URA3 protein of the other yeasts, showing high homologies, for example 73.4% to Saccharomyces cerevisiae, 76.3% to Kluyveromyces lactis, and 75.1% to Candida albicans.

Example 5 Cloning of the L41 Gene and Determination of the DNA Sequence of a DNA Fragment Containing the L41 Gene

Filters were prepared for about 30,000 colonies of the library prepared in Example 2 according to the method described in Molecular Cloning, 2nd edition, Sambrook et al., p. 12, 21-23, Cold Spring Harbor Laboratory (1989), and screened with a 1.1 kb ³²P-labelled XbaI—Sau3AI fragment containing Candida maltosa L41 gene, RIM-C, as a probe (Kawai et al., J. Bacteriol., 174, 254-262 (1992)).

Five positive clones were thus obtained. Restriction enzyme maps of the three clones, pCL41-1, pCL41-2 and pCL41-5 were constructed and compared with each other. These clones have a 4 kb EcoRI fragment in common (FIG. 8). Southern hybridization analysis of these plasmid DNA has revealed that a region which shows homology to the L41 gene of Candida maltosa is present in the 1.4 kb ClaI-PstI fragment within the 4 kb EcoRI fragment.

The 4 kb EcoRI fragment was inserted into the EcoRI site of pBluescript SK⁻ to prepare plasmids pCLE1 and pCLE2 in which the fragment is inserted to an opposite direction with each other. From these two plasmids, a variety of plasmids having deletion mutations were obtained by preparing deletion mutants with HindIII, XhoI or ClaI having a site within the EcoRI fragment or by preparing deletion mutants with ExoIII nuclease and mung bean nuclease in order to determine the 2086 bp DNA sequence from the BamHI site to the SacI site (FIG. 9).

Southern analysis revealed that a 318 bp open reading frame interrupted by a 367 bp intron is present in the region in which the presence of an L41 structural gene is deduced (FIGS. 8 and 10). At the 5′ and 3′ terminals and in the neighborhood of the 3′ terminal in the region which was deduced to be an intron, sequence (SEQ ID NO: 16) GTATGT-TACTAAC-AG which is common to intron was observed. Furthermore, the sequences were located at immediately after the initiation codon as well as six L41 genes of the other yeasts described by Kawai et al., J. Bacteriol., 174, 254-262 (1992); Pozo et al., Eur. J. Biochem., 213, 849-857 (1993)). The deduced amino acid sequence of the Candida utilis L41 polypeptide was compared with those of the L41 proteins of some other yeasts, showing high homologies, for example 93.4% to Saccharomyces cerevisiae L41, 89.6% to Candida tropicalis L41, and 85.8% to Candida maltosa L41.

Example 6 Preparation of Cycloheximide-resistance L41 Gene by Site-specific Mutation

The amino acid at 56 position of the L41 protein of a cycloheximide-resistant yeast is glutamine, while the amino acid at the corresponding position in the L41 protein of a cycloheximide-sensitive yeast is proline. It has been reported that the sensitivity to cycloheximide of the yeast is determined by this amino acid residue of the L41 protein (Kawai et al. , J. Bacteriol., 174, 254-262 (1992)). In addition, the amino acid at 56 of the L41 protein of a cycloheximide-sensitive Candida utilis was proline like that of a cycloheximide-sensitive Saccharomyces cerevisiae. The codon encoding the proline at the 56 position of the L41 gene was changed into a glutamine codon by site-specific mutagenesis in order to convert the L41 protein encoded by the gene into a cycloheximide-resistant protein, which was used as a selectable marker of transformation.

Firstly, a 2.1 kb BamHI-SacI fragment obtained from the plasmid pCLE1 was inserted between the BamHI and SacI sites of pUC18 to prepare a plasmid pCLBS1 (FIG. 11).

Furthermore, 0.6 kb fragment obtained by digesting the plasmid pCLE1 with AflII, treating with Klenow enzyme to form blunt ends and further digesting with Xhol was inserted between the SmaI and XhoI sites of pBluescript SK⁻ to prepare pCLAX1. In this plasmid, the AflII site is regenerated by the ligation of the blunt AflII end of the 0.6 kb fragment and the SmaI end of a vector. A single stranded DNA was prepared from PCLXA1 with a helper phage, and a mutant plasmid was prepared with a synthetic oligonucleotide (SEQ ID NO:17) 5′-TG TGG AAA ACT TGC TTG GTT TGA-3′ and a Sculptor In Vitro Mutagenesis Kit (Amersham). DNA sequence of the 0.6 kb insertion fragment on the candidate plasmid thus obtained was determined, and a plasmid pCLAX20 in which no mutation in the DNA sequence was found except that the 56th proline codon CCA had been mutated into a glutamine codon CAA was obtained.

A 0.6 kb insertion fragment was cut out as a ClaI-AflII fragment from pCLAX20 and ligated with a 4.4 kb fragment obtained by digesting the plasmid pCLBS1 with ClaI and AflII to construct a plasmid pCLBS10 containing a mutated L41 gene.

The plasmid pCLBS10 was digested with BamHI and SphI, treated with T4 DNA polymerase to form blunt ends, and NotI linkers (5′-AGCGGCCGCT-3′SEQ ID NO:18) were inserted to prepare a plasmid pCLBS12 (FIG. 11).

It was examined whether the mutated L41 gene thus obtained confers yeast resistance to cycloheximide or not. A 2.1 kb BamHI-SacI fragment containing the mutated L41 gene which was obtained from the plasmid pCLBS10 was inserted between the BamHI and SacI sites of YEp13K, a YEp vector (Sone et al., Appl. Environ. Microbiol., 54, 38-42 (1988)), to prepare a plasmid pYECL10. On the other hand, a 2.1 kb BamHI-SacI fragment containing the wild type L41 gene obtained from pCLBS1 was cloned into the YEp13K to prepare a plasmid pYECL1 as a control.

A Saccharomyces yeast strain YPH 500 was transformed with these plasmids according to the lithium acetate method described in Methods in Yeast Genetics—A Laboratory Course Manual—Rose M. D. et al., pp 122-123, Cold Spring Harbor Laboratory Press, NY (1990). Leucine non-requirement strains were selected as transformants. These transformants were grown on YPD plate containing cycloheximide. As a result, the strain retaining pYECL10 grew on the YPD plate containing cycloheximide. On the contrary, the strain retaining pYECL1 did not grow on the YDP plate containing cycloheximide. It was thus proved that the mutated L41 gene thus prepared conferred resistance to the cycloheximide-sensitive yeast.

Example 7 High-copy-number Integration of Vectors by Trancating the L41 Gene Promoter

(1) Construction of Promoter-deficient Mutants

Four kinds of rDNA fragments which were excised from plasmids pCRE2, pCRE3, pCRX1, and pCRX2 as shown in Example 2 (FIG. 2) by EcoRI or XbaI were inserted into the EcoRI and XbaI sites of the plasmid pCRBS10 (FIG. 11) described in Example 6 to construct plasmids pCLRE2, pCLRE3, pCLRX1, and pCLRX2 (FIG. 12). The structure of the plasmid pCLRE2 containing the C. utilis L41 gene, which is made to confer cycloheximide resistance by introducing site-specific mutation, and the C. utilis ribosomal DNA fragment is shown in FIG. 13a.

This plasmid (5 μg) was digested with PstI and BamHI, then extracted with phenol/chloroform to recover DNA by ethanol precipitation. The DNA was dissolved in 100 μl of ExoIII buffer (50 mM Tris-HCl (pH8.0), 100 mM NaCl, 5M M gCl₂, 10 mM 2-mercaptoethanol), 180 units of ExoIII nuclease were added, then the solution was maintained at 37° C. A sample (10 μl) was taken every minute and transferred into 10 μl of MB buffer (40 mM sodium acetate, 100 mM NaCl, 2 mM ZnCl₂ and 10% glycerol (pH 4.5)) in an ice-cold tube. Ten tubes thus prepared were maintained at 65° C. for 10 minutes to inactivate the enzymes, 5 units of mung bean nuclease was added, and the mixture was reacted at 37° C. for 30 minutes. After the reaction, the level of deletion was confirmed by agarose gel electrophoresis, and DNA fragments were recovered from five reaction solutions. The recovered DNA fragments were treated with Klenow enzyme to create blunt ends, a ligation reaction was carried out at 16° C. overnight, then transformation of E. coli was performed.

(2) Transformation and Analysis of Transformants

Transformation was carried out using a plasmid carrying the modified L41 gene containing −411 XhoI to +976 SacI and a plasmid carrying the modified L41 gene containing −1110 BamHI to +976 SacI. The transformation frequencies with these plasmids were virtually the same. Thus, the region downstream from the −411 XhoI site (where A at the initiation codon ATG is +1) was satisfactory as a promoter region for the expression of the L41 gene. Accordingly, 10 plasmids, pCLRE11 to pCLRE20 with deletions ranging from near the XhoI site to near the 3′ downstream translation initiation codon were selected. About 10 μg each of these plasmids were digested with BglII and used for transformation of C. utilis ATCC9950. Plasmids pCLRE11 to pCLRE20 were constructed in the same manner as pCLRE2. The transformation was carried out by the electric field pulse method (see WO/95/32289). Pulsing was performed at a capacitance of 25 μF, a resistance of 1,000 ohms, and a voltage of 5 KV/cm. Results showed that the transformation frequency decreased as the extent of deletion in the promoter region of the cycloheximide-resistance L41 gene increased. Specifically, the transformation frequencies were virtually the same with plasmids pCLRE11, pCRE12 and pCRE13, in which the extent of deletion was almost the same, but decreased with pCLRE14 to about 30%, with pCLRE15 and pCLRE16 to about 15%, and with pCLRE17 to about 0.3% of the frequency with pCLRE11 or 12. No transformants were obtained with pCLRE18, pCLRE19 and pCLRE20. In FIG. 13b, the 5′ ends of the L41 gene promoter region of the plasmids pCLRE11, pCLRE15, pCLRE16, pCLRE17, pCLRE18, pCLRE19 are indicated by arrows.

DNAs were prepared from the four independent clones, the transformants obtained with pCLRE15, pCLRE16 and pCLRE17 as well as pCLRE11. The DNAs were subjected to Southern blot analysis. A chromosomal DNA was prepared according to the method described in Methods in Yeast Genetics—A Laboratory Course Manual—Rose M. D. et al., pp131-132, Cold Spring Harbor Laboratory Press NY. The DNA thus prepared was digested with HindIII, subjected to agarose gel electrophoresis and then transferred to Hibond N+ Filter (Amersham) to prepare a filter for Southern hybridization. The filter on which the DNA was immobilized was prehybridized in a hybridization solution (6×SSC, 5×Denhardt solution, 0.2% SDS) at 65° C. for 2 hours.

Hybridization was next carried out using a 0.6 kb ClaI-HindIII fragment, which contained the L41 gene labeled with [α−³²P]dCTP (110 TBq/mmol) using Megaprime DNA labeling systems (Amersham), as a probe DNA at 65° C. for 16 hours. After the hybridization, the filter was washed in 1×SSC and 0.1% SDS at 65° C. for 2 hours and then subjected to autoradiography where signals were detected. A thick band derived from the integrated vectors was observed along with a band derived from the endogenous L41 gene. The number of copies of the integrated plasmids was estimated by comparing the intensity of the bands, assuming that the intensity of the band derived from the endogenous L41 gene corresponds to two copies since the number of copies for the C. utilis L41 gene has previously been proven to be 2 per cell. The intensity of the bands was measured using a BAS 2000 imaging analyzer (Fiji Film). FIG. 14 shows the results of Southern blot analysis and a graph showing the number of copies. While the number of copies of the plasmid pCLRE11 carrying the promoter region up to −420 was 9 to 14, the number of copies of the plasmids in which the promoter region was cut up to −190 (pCLRE15), −180 (pCLRE16) and −80 (pCLRE17) were 14 to 30 (pCLRE15), 17 to 42 (pCLRE16), and 35 to 90 (pCLRE17), respectively. Thus, it was shown that the number of copies integrated into the chromosome increased upon transformation in several vectors in which the marker gene, i.e., the promoter region of the cycloheximide-resistance L41 gene, was shortened.

Example 8 Construction of the Vectors for High-copy-number Chromosome Integration

(1) Construction of the Vectors Targeted at the rRNA Gene Locus

An approximately 1.2-kb fragment containing the ribosomal DNA obtained by digesting plasmid pCLRE2 with ApaI was cloned at the ApaI site of pBluescript SK (Stratagene) to construct plasmid pCRA1. This pCRA1 was then digested with XhoI and treated with Klenow enzyme to create blunt ends and then SphI linkers (5′-GGCATGCC-3′) were added to construct pCRA2. SphI-EcoRI fragments containing the L41 gene excised from plasmids pCLRE15, pCLRE16 and pCLRE17 were cloned between the SphI site and the EcoRI site of this plasmid to construct plasmids pCLR215, pCLR216 and pCLR217, respectively (FIG. 15).

Also, pCRA1 was digested with Asp718 and treated with Klenow enzyme to create blunt ends and then NotI linkers (5′-AGCGGCCGCT-3′ SEQ ID NO:18) were added to construct pCRA3. This plasmid was digested with NotI and BglII to obtain 0.5-kb and 0.7-kb NotI-BglII fragments. Moreover, pUC19 (Takara Shuzo) was digested with HindIII and EcoRI and treated with Klenow enzyme to create blunt ends and then BglII linkers (5′-CAGATCTG-3′) were added to construct plasmid pUCBgl. After digesting this plasmid with BglII, the two types of NotI-BglII fragments were cloned to construct pCRA10 (FIG. 16). In order to control the number of copies to be integrated into the chromosome, two fragments, with different lengths of promoter region, of the cycloheximide-resistance L41 gene, used as marker genes, were obtained by PCR. Specifically, the fragment from −405 to +974 and the fragment from −184 to +974 were obtained (where A in the initiation codon ATG is +1). These fragments were almost identical to the L41 gene fragment in plasmid pCLRE11 in which about 10 copies were integrated and that in plasmid pCLRE16 in which about 20 to 40 copies were integrated, respectively. In this case, the primers were designed to have an additional PstI site at the 5′ end of the primer and a SalI site at the 3′ end of the primer. Sequences of the primers used for the PCR were as follows:

5′-side primers for the L41 gene:

5′-CCTGCAGGAAACGTAAACAAAGAGGTTTCA-3′ (SEQ ID NO:19)

5′-CCTGCAGGCCCACGCAACACCTGGTGTCTG-3′ (SEQ ID NO:20)

3′-side primer for the L41 gene:

5′-GGTCGACTCGCTTTTGTGCGTGTGTGCATT-3′ (SEQ ID NO:21).

pCLRE2 was used as a template. Two amplified fragments were cloned into plasmid pT7Blue using the TA cloning kit (Invitrogen). These two kinds of fragments were excised as PstI-SalI fragments from the plasmids thus constructed and then ligated with pCRA10 to construct plasmid pCRAL10 containing the long L41 gene fragment and plasmid pCRAL11 containing the short L41 gene fragment.

In these plasmids pCRAL10 and pCRAL11, the integration target rDNA fragment is divided into two segments, and a sequence derived from plasmid pUC containing the Amp-resistance gene is integrated between the segments. Sincethis vector is used fortransformation after digestion at the BglII site, the resulting transformant incorporates the target DNA sequence and the marker gene therein, but not the DNA sequence derived from the plasmid pUC.

(2) Construction of the Vectors Targeted at the URA3 Gene Locus

Primers were designed based on the URA3 gene sequence of C. utilis (see Example 4), and two kinds of fragments containing the 5′ side and 3′ side of the URA3 gene were obtained by PCR.

A fragment from +4 to +354 (where A in the initiation codon ATG is +1) was obtained as the 5′ side fragment of the URA3 gene. In this case, the primers were designed to have an additional SalI site at the 5′ end of the primer and a BglII site at the 3′ end of the primer. Sequences of the primers were as follows:

5′-GGGTCGACATGTCACCACGTTATCGTACAC-3′ (SEQ ID NO:22)

5′-GGAGATCTGCCCATTGCGCAATCTT-3′ (SEQ ID NO:23)

A fragment from +356 to +685 was obtained as the 3′-side fragment of the URA3 gene. In this case, the primers were designed to have a BglII site at the 5′ end of the primer and a Asp718 (KpnI) site at the 3′ end of the primer. Sequences of the primers were as follows:

5′-GGAGATCTCACCAACGCCCACGGTGT-3′ (SEQ ID NO:24)

5′-GGGGTACCTAGCCACCACTGACAACCTCAT-3′ (SEQ ID NO:25)

The two amplified fragments thus obtained were cloned into plasmid pT7Blue using the TA cloning kit (Invitrogen). The 5′-side fragment and the 3′-side fragment of the URA3 gene were excised from the two kinds of constructed plasmids as a SalI-BglII fragment and a BglII-Asp718 fragment, respectively, and inserted between the SalI site and the Asp718 site of pUC19 (Takara Shuzo) to construct plasmid pURA1. The plasmid was modified to have a BglII site by changing the base A located at +355 in the open reading frame of the URA3 gene to C. The plasmid could be integrated into the URA3 gene on the chromosome by digesting the plasmid with BglII. Furthermore, the URA3 gene of pURA1 has a structure having partial deletions at the 5′-end region and 3′-end region of the open reading frame.

pURA1 was digested with Asp718 and treated with Klenow enzyme to create blunt ends and then NotI linkers (5′-AGCGGCCGCT-3′) SEQ ID NO:18 were ligated to construct plasmid pURA2. Furthermore, pURA1 was digested with HindIII and treated with Klenow enzyme to create blunt ends and then NotI linkers (5′-AGCGGCCGCT-3′, SEQ ID NO:18) were ligated to construct plasmid pURA3. Furthermore, pURA2 and pURA3 were digested with NotI and BglII to obtain two kinds of approximately 0.35-kb NotI-BglII fragments. These fragments were then cloned into the BglII-digested pUCBgl to construct pURA10 (FIG. 17).

Furthermore, two kinds of fragments of different length and containing the cycloheximide-resistance L41 gene obtained by PCR in (1) were ligated with pURA10 to construct plasmid pURAL10 containing the long L41 gene fragment and plasmid pURAL11 containing the short L41 gene fragment.

These plasmids pURAL10 and pURAL11 have the structure in which the integration target URA3 fragment is divided into two segments, and the sequence derived from plasmid pUC containing the Amp-resistance gene is integrated between the segments. Since this vector is used for transformation after digestion at the BglII site, the resulting transformant does not incorporate the DNA sequence derived from plasmid pUC.

(3) Construction of the Vector Targeted at the L41 Gene Locus

Vectors targeted at the (cycloheximide-resistance) L41 gene locus were constructed as follows. Two (cycloheximide-resistance) L41 gene fragments, approximately 380-bp (−85 to +292) and approximately 680-bp (+288 to +971), were obtained by PCR. The position of the 5′ end of the 5′-side fragment is almost identical to that of the 5′ end of the (cycloheximide-resistance) L41 gene promoter in pCLRE17. As such, for the fragment from −85 to +292, a PstI site was added to its 5′ side and a BglII site was constructed at the 3′ side by substituting T at +289 with G. Primers used for PCR were as follows:

5′-CCTGCAGACCGGTGAAATTTATCGAAA-3′ (SEQ ID NO:26)

5′-GAGATCTGATGATGCCTGTTGATATTCATC-3′ (SEQ ID NO:27)

As for the fragment from +288 to +971, PstI and NotI sites were added to its 3′ side and a BglII site was constructed at the 5′ side by substituting T at +289 with G. Primers used for PCR were as follows:

5′-GAGATCTCTACAATGGCTCGTTCCCA-3′ (SEQ ID NO:28)

5′-CCTGCAGGGCGGCCGCTTTTGTGCGTGTGTGCATTT-3′ (SEQ ID NO:29)

pCLRE2 was used as a template. Two amplified fragments were cloned into plasmid pT7Blue using the TA cloning kit (Invitrogen). These two kinds of fragments were excised as PstI-SalI fragments from the plasmids thus constructed and cloned into a BglII-digested pUCBgl to construct plasmid pCL12 (FIG. 18).

The plasmid pCL12 has the structure in which the L41 gene fragment, the integration target sequence, is divided into two segments, and the sequence derived from plasmid pUC containing the Amp-resistance gene is integrated between the fragments. Since this vector is used for transformation after the digestion at the BglII site, it is characterized in that the resulting transformants incorporate the target DNA sequences and the heterologous gene therein but not the DNA sequence derived from the plasmid pUC. Furthermore, since the marker gene is divided by the sequence derived from the plasmid pUC on the vector, cycloheximide-resistant transformants can be obtained only when this plasmid is integrated into the chromosome in a tandem form.

Example 9 Construction of the Monellin Expression Plasmid

(1) Cloning of the Glyceraldehyde-3-phosphate Dehydrogenase (GAP) Gene

The glyceraldehyde-3-phosphate dehydrogenase (GAP) gene from C. utilis was cloned by the hybridization method in which a known GAP gene from other organisms was used as a probe. The DNA library of the C. utilis chromosome constructed in Example 1 was used as the gene library. Afilterwaspreparedbyadsorbingabout20,000plaquesof phage DNA of the gene library according to the method described in Molecular Cloning 2nd Edition, p2, 95-121, Cold Spring Harbor Laboratory, 1989. An approximately 1-kb AsuII-AflII fragment was then excised from the pUC18 plasmid carrying a 2.1 kb HindIII fragment containing the GAP gene of S. cerevisiae (Yamano et al., Journal of Biotechnology, 32, 165-171, 1994) as a DNA fragment containing most of the GAP gene. This fragment was labeled with ³²P and hybridization was carried out using this fragment as a probe. As a result, three positive plaques were isolated. A phage DNA of one of these plaques was subcloned and a 6.5-kb EcoRI fragment contained in this phage DNA was isolated and then integrated at the EcoRI site of the plasmid vector pBluescript IISK+ to construct plasmids pGAP1 and pGAP2 (FIG. 19).

(2) Construction of Plasmids Containing the GAP Gene Promoter/Terminator

The promoter and terminator fragments of the C. utilis glyceraldehyde-3-phosphate hydrogenase (GAP) gene were obtained by PCR using the plasmid pGAP1 as a template. For the promoter, a 974-bp fragment from −976 upstream of the initiation codon to −1 immediately before the initiation codon (where A in the initiation codon is +1) was obtained using the following primers.

5′-AGCGGCCGCTAGCTTACAGCGAGCACTCAAATCTGCCC-3′ (SEQ ID NO:30)

5′-GGGATCCTCTAGATATGTTGTTTGTAAGTGTGTTTTGTATC-3′ (SEQ ID NO:31)

In these primers, a NotI site was added to the end of the 5′-side primer and a XbaI and BamHI sites were added immediately before the 3′-side initiation codon. A 723-bp fragment from +1006 to +1728 immediately after the termination codon was obtained as the terminator. The following primers were used, and a BamHI site was added immediately after the termination codon at the 5′ side and a PstI site was added to the 3′ side.

5′-GGGGATCCATTGTATGACTTTTATTTATGG-3′ (SEQ ID NO:32)

5′-CCCTGCAGGGATAAAGCTGAAGAATAAT-3′ (SEQ ID NO:33)

Two amplified fragments thus obtained were cloned into plasmid pT7Blue using the TA cloning kit (Invitrogen). These two fragments were obtained as a NotI-BamHI fragment and a BamHI-PstI fragment, which were then cloned between the NotI and PstI sites of the pBluescript SK− to construct plasmid pGAPPT10 (FIG. 20).

(3) Construction of the Plasmids for Expression of the Monellin Gene and Transformation

The monellin gene was excised as a DraI-BglII fragment from the plasmid pMNY1 containing a synthetic DNA sequence corresponding to the amino acid sequence shown in SEQ ID NO. 5. Briefly, pMNY1 can be obtained by inserting a chemically synthesized DNA fragment corresponding to the amino acid sequence of SEQ ID NO. 5 between the EcoRI site and the HindIII site of pUC18 (Pharmacia) (see Japanese Patent Laid-open 1993/70494). The plasmid pGAPPT10 was digested with XbaI, treated with Klenow enzyme to create blunt ends, then further digested with BamHI. The resulting fragment was ligated with the DraI-BglII fragment containing the monellin gene to construct plasmid pGAPM3 (FIG. 20). Furthermore, the NotI-PstI fragments excised from pGAPM3 were ligated into the PstI and NotI sites of plasmids pCLR215, pCLR216, pCLR217, pCRAL10, pCRAL11, pURAL10, and pURAL11 described in Example 2 to construct plasmids pCLRM215, pCLRM216, pCLRM217, pRM10, PRM11, pUM10, and pUM11 (FIG. 20). These seven kinds of plasmids thus constructed were digested with BglII and then used for transformation of C. utilis strain ATCC9950 by the electric field pulse method as described in Example 1. As a result, transformants with pCLRM215, pCLRM216, pRM10, pRM11, pUM10, and pUM11 were obtained. No transformant was obtained for pCLRM217.

Example 10 Expression of Monellin in Yeast Transformants

Four strains each of the transformants with pCLRM215, pCLRM216, pRM10, pRM11, pUM10, and pUM11 were cultured in 10 ml of YPD medium for 24 hours with shaking. Cells were collected by centrifugation, suspended in 50 mM Tris (pH 7.5), 15 mM NaCl, 1 mM DTT, and 1mM PMSF, and then disrupted by vortexing with glass beads. Cell debris and insoluble precipitates were removed by centrifugation at 15,000×g for 10 minutes to derive soluble proteins. The soluble proteins thus prepared were subjected to 15/25% SDS-PAGE and the expression was analyzed. A band was found for all plasmids at a position corresponding to a molecular weight of about 10,000 which corresponds to monellin. The results further showed that transformants with high-copy-type pCLRM215, pCLRM216, pRM11, and pUM11 were expressed at a remarkably higher level as compared to transformants with low-copy-type pRM10 and pUM10. Whole soluble proteins of two strains each of C. utilis transformants with pCLRM216, pRM11 and pUM11 were subjected to electrophoresis on 15/25% SDS-PAGE. Results are shown in FIG. 21 (1).

As a control, transformants with plasmid pCLRE4 containing the rDNA fragment and the cycloheximide-resistance L41 gene were similarly treated. The pCLRE4 was constructed by inserting a 3.5-kb EcoRI fragment obtained from pCRE2 (FIG. 2) described in Example 2 into the EcoRI site of the plasmid pCLBS12 (FIG. 11) described in Example 6. The gel was stained with Coomassie Brilliant Blue after electrophoresis, dried and then scanned by a densitometer to calculate the percentage of monellin in the total soluble proteins. It was found that monellin had accumulated to a level of about 50% of the cellular soluble proteins in C. utilis transformants with pCLRM216, pRM11 and pUM11, and that the expression level tended to increase in transformants with pUM11 and pRM11 in which sequences derived from bacteria were deleted.

On the other hand, monellin expression in yeast S. cerevisiae was studied using yeast TD4 (a mutant strain (a, his, ura, leu, tryp) of S. cerevisiae S288c (ATCC 26108)) (see Japanese Patent Laid-open 1993/70494) which was transformed with the plasmid pCTMNY1 containing an expression cassette consisting of “GAP promoter+monellin gene+PGK terminator” and the TRP1 gene as a marker, and the full length of yeast 2 μm DNA. Two strains of transformants thus transformed were cultured in 10 ml of SD medium (0.67% yeast nitrogen base (free of amino acid), 2% glucose) containing histidine, uracil and leucine (20 μg/ml each) at 30C for 24 hours with shaking. Furthermore, cells of the parent strain TD4 were similarly cultured in the abovementioned medium supplemented with tryptophan. Soluble protein fractions were prepared and subjected to electrophoresis on 15/25% SDS-PAGE. Results are shown in FIG. 21 (2). Monellin expression was calculated to be about 5% of the total soluble protein by quantitative densitometer measurements. It was shown that the level of monellin expression of S. cerevisiae transformants with pCTMNY1 was remarkably low as compared to expression of C. utilis transformants in spite of the fact that monellin was expressed in S. cerevisiae transformants with YEp-type plasmids deemed to be present in more than 50 copies per cell using the powerful GAP promoter. Furthermore, the amount of monellin expressed was about 10% of the cellular proteins when the monellin gene was expressed in E. coli under the control of the TRP gene promoter (see Japanese Patent Laid-open 1993/70494). From these results, it was revealed that C. utilis is a suitable host for the expression of heterologous proteins.

DNAs were prepared from the four clones, the transformants obtained with pCLRM216, pRM11, and pUM11 and subjected to Southern blot analysis. The DNAs for pCLRM216 and pRM11 were digested with PstI+EcoRI, the DNA for pUM11 was digested with HindIII, and a 0.6-kb ClaI-HindIII L41 gene fragment was used as a probe for the analysis. The number of copies of the integrated plasmids was estimated assuming that the intensity of the band derived from the endogenous L41 gene corresponds to 2 copies. The intensity of the bands was measured using a BAS 2000 imaging analyzer (Fiji Film). The calculated numbers of copies of the integrated plasmids were 10 to 19 copies for the pCLRM216 transformants, 12 to 18 copies for the pRM11 transformants, and 17 to 27 copies for the pUM11 transformants.

Southern blot analysis with the same filter using pUC19 as a probe showed that no DNA sequence from bacteria was integrated into the chromosome for the pRM11 and pUM11 transformants.

The four clones each of the pCLRM216, pRM11, and pUM11 transformants were consecutively subcultured in YPD liquid medium to study the stability of the integrated genes. First, cells grown on YPD plate supplemented with cycloheximide were inoculated into 10 ml of YPD liquid medium and cultured to the stationary phase. Then, 10 μl of the resulting culture was inoculated into 10 ml of fresh YPD liquid medium and then cultured to the stationary phase. Subcultures in this nonselective medium were repeated four times for about 50 generations of growth. Cells were collected from the last culture, suspended in 50mM Tris (pH 7.5), 150 mM NaCl, 1 mM DTT, and 2 mM PMSF, and disrupted by vortexing with glass beads to prepare soluble proteins. The whole soluble proteins from the four clones each of pCLRM216, pRM11, and pUM11 transformants were subjected to 15/25% SDS-PAGE. Results are shown in FIG. 22.

The results show that the level of monellin expression decreased in the strains transformed with pCLRM216 and pRM11, though it was variable, while no marked decrease was observed in the four clones transformed with pUM11. Furthermore, the subculture of 50 generations was diluted and plated on YPD plates and YPD plates supplemented with 40 μg/ml cycloheximide. After incubation for 2 days at 30° C., colonies were counted to estimate the ratio of cells grown on the latter plates to cells grown on the former plates.

Results were 0, 2.0, 2.3 and 4.0% for the four clones of pCLRM216 transformants, 1.0, 1.0, 4.7 and 7.2% for the four clones of pRM11 transformants, and 97.0, 100, 40.2 and 43.5% for the four clones of pUM11 transformants, which showed that pUM11 was extremely stable as compared to the other two plasmids. These results showed that the plasmid pUM11 was particularly superior among the developped vectors in terms of its expected copy number and stability, although observed ratios do not exactly reflect the retention capability of the plasmid because the cells could become cycloheximide sensitive even if only a part of the integrated plasmid is lost from the chromosome.

Example 11 Purification of Monellin

The pUM11 transformants were incubated in YPD medium at 30° C. overnight with shaking and then the resulting cells were collected by centrifugation. To about 10 g by wet weight (corresponding to 2 g by dry weight) of the cells, 17 ml of 0.9 M sorbitol were added, and the resulting cell suspension was incubated at 37° C. for 30 minutes with an addition of 6 ml of Zymolyase 100T (Seikagaku Corp.) with stirring. The cell suspension was treated with a french press (1,000 psi, 3 times) to disrupt the cells. A supernatant fraction was obtained by centrifugation (10,000×g, 20 minutes). The precipitate fraction was washed three times with a sodium phosphate buffer solution (10 mM sodium phosphate (pH 7.0), 100 mM NaCl) to collect another supernatant fraction, which was combined with the previously obtained supernatant fraction. This fraction thus combined was called the french press-treated sample. Similarly, in order to compare disruption efficiency, 10 g (by wet weight) of the cells were destroyed with dynomill for 15 minutes while cooling with 40 ml of a sodium phosphate buffer solution (10 mM sodium phosphate (pH 7.0), 100 mM NaCl) and 60 ml of glass beads (425 to 600 microns, Sigma). A supernatant fraction of this crushed material was collected. The glass beads were thoroughly washed with the abovementioned buffer solution until no protein was extracted. This wash and the previously obtained supernatant fraction were combined, which was called the dynomill-treatedsample. Thefrench press-treated fraction and the dynomill-treated fraction were subjected to SDS-PAGE to compare the efficiency of monellin extraction. Results showed there was no significant difference between the two treatments.

Preliminary experiments on acid and heat treatments for monellinpurificationwereperformed. The dynomill-treated sample was diluted to a protein concentration of 1.5 mg/ml (all the proteins were quantified by a Bio-Rad protein assay kit using BSA as a standard). Acid treatment was carried out by adjusting the pH of the sample to 4, 4.5, or 5.5 with the addition of a 40 mM sodium acetate buffer solution and maintaining the solution at 4° C. for 12 hours. Heat treatment was carried out by heating the sample at 50° C., 60° C., or 70° C. for 10 minutes. Results showed that undesirable proteins derived from yeast, other than monellin, were copiously precipitated by the acid treatment at pHs 4 and 4.5 or by the heat treatment at 60° C. for 10 minutes.

It was also found that heat treatment at 50° C. for 10 minutes was not effective, and that heat treatment at 70° C. for 10 minutes precipitated monellin along with other proteins. Furthermore, it was found that nearly 100% of non-monellin proteins could be removed by combining the heat treatment at 60° C. for 10 minutes and the acid treatment at pH 4. Results of SDS-PAGE is shown in FIG. 23. Based on these experimental results, monellin was purified using the french press-treated sample. The french press-treated sample was diluted with a sodium phosphate buffer solution (10 mM sodium phosphate (pH 7.0), 100 mM NaCl) to adjust the protein concentration to about 2.0 mg/ml and then heated at 50° C. for 10 minute in a water bath. After removing the precipitates by centrifugation, the pH of the resulting solution was adjusted to 4.5 by adding 200 mM sodium acetate buffer (pH 3.0) with stirring, and acid treatment was carried out while cooling. After treatment for about 1 hour, the pH was adjusted to 6.0 by the addition of 200 mM sodium phosphate buffer (pH7.0). After removing the precipitates by centrifugation, the supernatant fraction was concentrated by ultrafiltration (molecular weight 3,000 cut), then dialyzed against 10 mM sodium phosphate buffer (pH 7.0) overnight. The insoluble fraction was removed by centrifugation followed by filtration through a 0.2 micron filter (Millipore), after which the resulting fraction was passed through a column (50 ml) of CM-Sepharose (Pharmacia) equilibrated with the buffer. The unadsorbed fraction was eluted with the same buffer and the target protein was obtained with a linear gradient of 0 to 0.4 M NaCl solution (150 ml). This target protein was subjected to SDS-PAGE, and with the presence of a single band on the gel, was confirmed to be purified (see FIG. 23).

The circular dichroism spectrum (wave length from 190 nm to 260 nm) of natural monellin shows a strong negative spectrum near 212 nm and a positive spectrum at near 236 nm. A circular dichroism spectrum of the purified recombinant monellin was very similar to that of natural monellin.

Purified single-chain monellin and natural monellin samples were each dissolved in pure water to concentrations of 0.3 μg/μl, 0.2 μg/μl, 0.1 μg/μl, 0.05 μg/μl, and 0.02 μg/μl and 10 μl of each solution were used to evaluate sweetness by a taste test on the tongue. The sweetness threshold concentrations for the natural and recombinant were the same, 0.05 to 0.1 μg/μl (i.e., 0.5 to 1 μg protein), indicating that monellin produced in yeast had a specific activity equivalent to that of natural monellin.

Example 12 Synthesis of the Amylase Gene

The amino acid sequence encoded by the amylase gene derived from Sulfolobus solfataricus KM1 (Kobayashi K. et al., Biosci. Biotech. Biochem., 60(10), 1720-1723, 1966), was converted to the DNA sequence using those codons, except those for methionine and tryptophane, most frequently used in the glyceraldehyde-3-phosphoric acid dehydrogenase (GAP) gene of C. utilis. The DNA sequence was designed such that the variation in codons for each amino acid contained in the gene would be as close as possible to that for GAP, that specific restriction enzyme sites would be formed at intervals of about 180 to 320 bases, and that the gene would be constructed as a group of several segments. Some minor codons were also used to conveniently form the restriction enzyme cleavage sites. In addition, the sequence was designed to have an XbaI recognition site on the 5′ upstream side one base distant from the translation initiation codon (ATG) of the structural gene and a BglII recognition site on the 3′ downstream side one base distant from the translation termination codon. Taking these design parameters into consideration, the gene encoding the amylase from S. solfataricus KM1 was constructed to consist of seven segments, A-1 to A-7 (SEQ. ID. NO. 7 to 13). Each segment has specific restriction enzyme recognition sites at both ends and additional two nonsense nucleotides at both ends of the restriction enzyme recognition sites to enable each segment to be digested directly by the restriction enzymes. Primers used in the synthesis of each segment are shown in FIGS. 24, 25 and 26.

The segments A-1 to A-7 were synthesized as follows. PCR was carried out using ExTaq polymerase (Takara Shuzo) with 1/10 of the dNTP amount indicated in the manual (20 μM each of dA, dG, dC, and dT) for 25 cycles of reaction at 94° C. for 30 second and at 72° C. for 90 seconds, or for 25 cycles of reaction at 94° C. for 30 seconds, at 55-65° C. for 60 seconds, and at 72° C. for 60 seconds. The PCR reaction to produce double-stranded DNA in the following synthesis of the gene was carried out under the same conditions, except that the primers and template DNAs were different.

Segment A-1 (SEQ ID NO. 7), a 288-bp fragment having XbaI and StyI sites at both ends was made from four oligonucleotides. First, PCR was carried out using primers A-1-2 and A-1C-2. Another PCR was carried out using the reaction solution obtained by this PCR as a template using primers A-1-1 and A-1C-1 to obtain a 282-bp double-stranded DNA.

Segment A-2 (SEQ ID NO. 8), a 312-bp fragment having StyI and AccI sites at both ends, was also made from four oligonucleotides. First, PCR was carried out using primers A-2-2 and A-2C-2. Another PCR was carried out using the synthesized double-stranded DNA as a template using primers A-2-1 and A-2C-1 to obtain a 312-bp fragment.

Segment A-3 (SEQ ID NO. 9), a 241-bp fragment having AccI and XhoI sites at both ends, was also made from four oligonucleotides.

First, PCR was carried out using primers A-3-2 and A-3C-2. Another PCR was carried out using the synthesized double-stranded DNA as a template using primers A-3-1 and A-3C-1 to obtain a 214-bp fragment.

Segment A-4 (SEQ ID NO. 10), a 214-bp fragment having XhoI and EcoRV sites at both ends, was also made from four oligonucleotides. First, PCR was carried out using primers A-4-2 and A-4C-2. Another PCR was carried out using the synthesized double-stranded DNA as a template using primers A-4-1 and A-4C-1 to obtain a 214-bp fragment.

Segment A-5 (SEQ ID NO. 11), a 184-bp fragment having EcoRV and SalI sites at both ends, was made from two oligonucleotides. PCR was carried out using primers A-5-1 and A-5C-1 to obtain a 184-bp fragment.

Segment A-6 (SEQ ID NO. 12), a 241-bp fragment having SalI and CClaI sites at both ends, was also made from four oligonucleotides. First, PCR was carried out using primers A-6-2 and A-6C-2. Another PCR was carried out using the synthesized double-stranded DNA as a template using primers A-6-1 and A-6C-1 to obtain a 241-bp fragment.

Segment A-7 (SEQ ID NO. 13), a 284-bp fragment having ClaI and BglII sites at both ends, was also made from four oligonucleotides. First, PCR was carried out using primers A-7-2 and A-7C-2. Another PCR was carried out using the synthesized double-stranded DNA as a template using primers A-7-1 and A-7C-1 to obtain a 284-bp fragment.

The seven fragments thus amplified were cloned into pT7Blue vector (Invitrogen), or the HincII site of pUC118 after treated with a Klenow enzyme and phosphorylated. DNA sequences of these seven fragments were determined and confirmed to be identical to the designedsequences. Thesefragments were digested with individual restriction enzymes which recognized respective ends, recovered using a low melting point agarose gel (FMC BioProducts), and then purified using β-Agarase-I (Japan Gene).

These seven fragments were ligated with each other as follows: Three fragments, segments A-1, A-2, and A-3 were simultaneously inserted into the XbaI and XhoI sites of pBSIIKS+. The resulting plasmid was named pAmy123. XbaI and XhoI fragments containing segments A-1, A-2, and A-3 were recovered from this plasmid and inserted between the XbaI and EcoRV sites of pBSIIKS+ along with segment A-4, i.e., the XhoI-EcoRV fragment. The resulting plasmid was named pAmy1234. The XbaI-EcoRV fragment containing segments A-1 to A-4 was recovered from this plasmid and inserted between the XbaI and SalI sites of pBSIIKS+ along with an EcoRV-SalI fragment containing segment A-5. This plasmid was named pAmy12345. A vector (called pBSBgl) was prepared by inserting BglII linkers (CAGATCTG) at the SmaI site of pBSIIKS+. Segments A-6 and A-7 were inserted between the BglII and SalI sites of this vector. The resulting plasmid was named pAmy67. The HindIII and PstI sites of pUC12 were treated with Klenow enzyme and BglII linkers (CAGATCTG) were inserted; the resulting vector (called pUC12BglII) was digested with XbaI and BglII. The XbaI-SalI region containing segments A-1 to A-5 from the abovementioned pAmy12345 and the SalI-BglII region containing segments A-6 and A-7 from pAmy67 were simultaneously inserted into this plasmid and thus the synthesis of the gene encoding the amylase from S. solfataricus KM1 strain (SEQ ID NO. 14) was completed.

Example 13 Construction of the Amylase Expression Cassette and Transformation

The XbaI-BglII fragment of the gene encoding amylase derived from S. solfataricus KM1 strain was inserted between the XbaI and BamHI sites of pGAPPT10. This plasmid was named pGAPUA. An approximately 3.4-kb expression cassette containing the amylase gene flanked by the GAP promoter and the GAP terminator was recovered as a NotI-PstI fragment. This approximately 3.4-kb fragment derived from pGAPUA was inserted at the PstI/NotI sites of pURAL11, pCRAL11, and pCL12 obtained in Example 8 to construct plasmids pURAL11UA, pCRAL11UA, and pCL12UA, respectively (FIG. 27). After digesting these plasmids with restriction enzyme BglII, cells of C. utilis ATCC9950 were transformed by the electric pulse method as described in Example 7. Conditions for pulsing were a capacitance of 25 μF, resistance of 1,000 ohms, and voltage of 5 KV/cm.

Example 14 Expression of Amylase in Yeast Transformants

The transformants with plasmids pURAL11UA, pCRAL11UA, and pCL12UA were cultured in YPD liquid medium for one day, after which soluble proteins were extracted from the collected cells according to the method described in Example 10 and were subjected to SDS-PAGE. In all cases, amylase had accumulated in an amount more than 50% of the soluble proteins. Soluble proteins extracted from three transformants with pURAL11UA and one transformant with a plasmid containing the cycloheximide-resistance gene (pCLRE2) were subjected to 4/20% SDS-PAGE. Since the present amylase is thermostable, samples of these soluble proteins were heated at 70C for 30 minutes and were similarly subjected to 4/20% SDS-PAGE. Results are shown in FIG. 28. The heat-treated samples showed the same specific amylase activity as that derived from S. solfataricus KM1 strain. There was not much difference between amylase production calculated from the activity based on the specific activity of the purified enzyme standard preparation and the production estimated from the results of SDS-PAGE, which indicated that the amylase produced in the yeast cells was of the active form.

Furthermore, transformants with pCRAL11UA, pURAL11UA, and pCL12UA were cultured for about 50 generations in a nonselective medium according to the method described in Example 10 to study the stability of the integrated genes. Results showed that production markedly decreased in 3 out of 5 clones transformed with pCRAL11UA which used rDNA as the target for integration, while the production did not markedly change in the clones transformed with pURAL11UA and pCL12UA which used the URA3 gene locus and the L41 gene locus respectively, as the target for integration. These results demonstrated that the plasmids integrated using the L41 gene locus as the target for integration were of equal excellence in high level expression of the gene by high-number-copy integration and in degree of stability as those integrated using the URA3 gene locus as the target.

Example 15 Expression of GIF

Human glycosylation inhibiting factor (GIF) is a protein mainly produced in T cells. Comprised of 115 amino acids, it has a molecular weight of 12,500 and is known to have immuno suppressive activity (Mikayama et al., Proc. Natl. Acad. Sci., USA, 90, 10056-10060, 1993). A 348-bp DNA was synthesized based on this amino acid sequence using codons most frequently used in C. utilis. An NheI site was added to the 5′ end and a BglII site was added to the 3′ end. The resulting 350-bp fragment was ligated with plasmid pGAPPT10 (Example 3) digested with XbaI and BamHI to construct pGAPGIF1 (FIG. 29).

Also, the 1.2-kb PstI-SalI cycloheximide-resistance L41 gene fragment described in Example 2 was inserted between the XhoI and PstI sites of plasmid pCRA1 to construct plasmid pCRAL2. A GAP promoter+GIF gene+GAP terminator fragment which was excised from plasmid pGAPGIF1 as a NotI-PstI fragment was inserted between the NotI and PstI sites of this plasmid pCRAL2 to construct plasmid pRALGIF2 (FIG. 29).

This plasmid was digested at the BglII site within the rDNA fragment, then cells of C. utilis ATCC 9950 were transformed by the electric pulse method as described in Example 7. Cells of eight clones of the resulting transformants were cultured in 10 ml of YPD medium for 24 hours with shaking. The cells were collected by centrifugation, suspended in 50 mM Tris (pH 7.5), 150 mM NaCl, 1 mM DTT, and 1 mM PMSF, and disrupted by vortexing with glass beads. Cell debris and insoluble precipitates were removed by centrifugation at 15,000×g for 10 minutes to prepare soluble proteins. The resulting soluble proteins were subjected to electrophoresis on 15% to 25% SDS-PAGE to study GIF expression. Results showed the presence of a band at a position corresponding to a molecular weight of about 12,000 which corresponds to GIF.

66 1 192 DNA Candida utilis 1 aacacccacc cacgcaacac ctggtgtctg gatgttgacg ctttgtatgc gtgtgtgtgt 60 tttttcttcc gtcttgttgg gccactctgc gcgagcgttg gcgactcacc ggtgaaattt 120 atcgaaaact ttcaggctca ggcccttttc aacactaccc tttgagatca catcaagcag 180 taatcaaaca ca 192 2 184 DNA Candida utilis 2 cccacgcaac acctggtgtc tggatgttga cgctttgtat gcgtgtgtgt gttttttctt 60 ccgtcttgtt gggccactct gcgcgagcgt tggcgactca ccggtgaaat ttatcgaaaa 120 ctttcaggct caggcccttt tcaacactac cctttgagat cacatcaagc agtaatcaaa 180 caca 184 3 82 DNA Candida utilis 3 ggtgaaattt atcgaaaact ttcaggctca ggcccttttc aacactaccc tttgagatca 60 catcaagcag taatcaaaca ca 82 4 291 DNA Artificial Sequence Description of Artificial Sequence Synthetic DNA 4 atg ggc gag tgg gaa atc atc gat atc ggt cca ttc act caa aac ttg 48 Met Gly Glu Trp Glu Ile Ile Asp Ile Gly Pro Phe Thr Gln Asn Leu 1 5 10 15 ggt aaa ttc gct gtt gat gaa gaa aac aag att ggc caa tac ggt aga 96 Gly Lys Phe Ala Val Asp Glu Glu Asn Lys Ile Gly Gln Tyr Gly Arg 20 25 30 ttg acc ttt aac aag gtt atc aga cca tgc atg aag aag act att tac 144 Leu Thr Phe Asn Lys Val Ile Arg Pro Cys Met Lys Lys Thr Ile Tyr 35 40 45 gaa aac gaa ggt ttt aga gaa att aag ggt tac gaa tac caa ttg tac 192 Glu Asn Glu Gly Phe Arg Glu Ile Lys Gly Tyr Glu Tyr Gln Leu Tyr 50 55 60 gta tac gct tct gac aag ttg ttc cgt gct gac att tcc gaa gac tac 240 Val Tyr Ala Ser Asp Lys Leu Phe Arg Ala Asp Ile Ser Glu Asp Tyr 65 70 75 80 aag aca cgt ggt cgt aag ttg ttg aga ttc aac ggt cca gtc cca cca 288 Lys Thr Arg Gly Arg Lys Leu Leu Arg Phe Asn Gly Pro Val Pro Pro 85 90 95 cca 291 Pro 5 97 PRT Artificial Sequence Description of Artificial Sequence Synthetic protein 5 Met Gly Glu Trp Glu Ile Ile Asp Ile Gly Pro Phe Thr Gln Asn Leu 1 5 10 15 Gly Lys Phe Ala Val Asp Glu Glu Asn Lys Ile Gly Gln Tyr Gly Arg 20 25 30 Leu Thr Phe Asn Lys Val Ile Arg Pro Cys Met Lys Lys Thr Ile Tyr 35 40 45 Glu Asn Glu Gly Phe Arg Glu Ile Lys Gly Tyr Glu Tyr Gln Leu Tyr 50 55 60 Val Tyr Ala Ser Asp Lys Leu Phe Arg Ala Asp Ile Ser Glu Asp Tyr 65 70 75 80 Lys Thr Arg Gly Arg Lys Leu Leu Arg Phe Asn Gly Pro Val Pro Pro 85 90 95 Pro 6 97 PRT Candida utilis 6 Met Gly Glu Trp Glu Ile Ile Asp Ile Gly Pro Phe Thr Gln Asn Leu 1 5 10 15 Gly Lys Phe Ala Val Asp Glu Glu Asn Lys Ile Gly Gln Tyr Gly Arg 20 25 30 Leu Thr Phe Asn Lys Val Ile Arg Pro Cys Met Lys Lys Thr Ile Tyr 35 40 45 Glu Glu Asn Gly Phe Arg Glu Ile Lys Gly Tyr Glu Tyr Gln Leu Tyr 50 55 60 Val Tyr Ala Ser Asp Lys Leu Phe Arg Ala Asp Ile Ser Glu Asp Tyr 65 70 75 80 Lys Thr Arg Gly Arg Lys Leu Leu Arg Phe Asn Gly Pro Val Pro Pro 85 90 95 Pro 7 282 DNA Artificial Sequence Description of Artificial Sequence Synthetic DNA 7 ggtctagata tgaccttcgc ttacaagatc gatggtaacg aggttatctt cactttgtgg 60 gctccatacc aaaagtccgt taagttgaag gtcttggaga agggtttgta cgagatggag 120 agagacgaga agggttactt caccatcact ttgaacaacg tcaaggtcag agacagatac 180 aagtacgttt tggacgatgc ttccgagatc ccagacccag cttccagata ccaaccagag 240 ggtgtccacg gtccatctca aatcatccaa gagtccaagg cc 282 8 312 DNA Artificial Sequence Description of Artificial Sequence Synthetic DNA 8 aaccaaggag ttcaacaacg agaccttctt gaagaaggag gacttgatca tctacgagat 60 ccacgtcggt actttcaccc cagagggtac tttcgagggt gtcatcagaa agttggacta 120 cttgaaggat ttgggtatca ccgctatcga gatcatgcca atcgctcaat tcccaggtaa 180 gagagactgg ggttacgatg gtgtttactt gtacgctgtc caaaactcct acggtggtcc 240 agagggtttc agaaagttgg ttgatgaggc tcacaagaag ggtttgggtg ttatcttgga 300 cgttgtctac tt 312 9 241 DNA Artificial Sequence Description of Artificial Sequence Synthetic DNA 9 atgtctacaa ccatgttggt ccagagggta actacatggt taagttgggt ccatacttca 60 gtcaaaagta caagacccca tggggtttga ccttcaactt cgacgacgct gagtccgatg 120 aggtcagaaa gttcatcttg gagaacgttg aatactggat caaggagtac aacgttgatg 180 gtttcagatt ggacgctgtc cacgctatca tcgacacctc tccaaagcac atcctcgagg 240 a 241 10 214 DNA Artificial Sequence Description of Artificial Sequence Synthetic DNA 10 tcctcgagga gatcgctgat gttgtccaca agtacaacag aatcgttatc gctgagtccg 60 acttgaacga cccacgtgtt gttaacccaa aggagaagtg tggttacaac atcgacgctc 120 aatgggttga cgatttccac cactctatcc acgcttactt gaccggtgag agacaaggtt 180 actacactga cttcggtaac ttggacgata tcgt 214 11 184 DNA Artificial Sequence Description of Artificial Sequence Synthetic DNA 11 acgatatcgt taagtcctac aaggacgtct tcgtttacga tggtaagtac tccaacttca 60 gaagaaagac ccacggtgag ccagttggtg agttggatgg ttgtaacttc gtcgtttaca 120 tccaaaacca cgatcaagtc ggtaacagag gtaagggtga gagaatcatt aagctcgtcg 180 actt 184 12 241 DNA Artificial Sequence Description of Artificial Sequence Synthetic DNA 12 tcgtcgacag agagtcctac aagatcgctg ctgctttgta cttgttgtct ccatacatcc 60 caatgatctt catgggtgag gagtacggtg aggagaaccc attctacttc ttctctgact 120 tctccgactc caagttgatc caaggtgtta gagagggtag aaagaaggag aacggtcaag 180 acactgatcc acaagacgag tccaccttca acgcttccaa gttgtcttgg aagatcgatg 240 a 241 13 284 DNA Artificial Sequence Description of Artificial Sequence Synthetic DNA 13 agatcgatga ggagattttc agtttctaca agatccttat caagatgaga aaggagttgt 60 ccatcgcttg tgacagaaga gtcaacgttg tcaacggtga gaactggttg atcatcaagg 120 gtagagaata cttctccttg tacgtcttca gtaagtcctc catcgaggtt aagtacagtg 180 gtaccttgtt gttgtcttcc aacaacagtt tcccacaaca catcgaggag ggtaagtacg 240 agttcgacaa gggtttcgct ttgtacaagt tgtagcagat ctgg 284 14 1680 DNA Artificial Sequence Description of Artificial Sequence Synthetic DNA 14 atg acc ttc gct tac aag atc gat ggt aac gag gtt atc ttc act ttg 48 Met Thr Phe Ala Tyr Lys Ile Asp Gly Asn Glu Val Ile Phe Thr Leu 1 5 10 15 tgg gct cca tac caa aag tcc gtt aag ttg aag gtc ttg gag aag ggt 96 Trp Ala Pro Tyr Gln Lys Ser Val Lys Leu Lys Val Leu Glu Lys Gly 20 25 30 ttg tac gag atg gag aga gac gag aag ggt tac ttc acc atc act ttg 144 Leu Tyr Glu Met Glu Arg Asp Glu Lys Gly Tyr Phe Thr Ile Thr Leu 35 40 45 aac aac gtc aag gtc aga gac aga tac aag tac gtt ttg gac gat gct 192 Asn Asn Val Lys Val Arg Asp Arg Tyr Lys Tyr Val Leu Asp Asp Ala 50 55 60 tcc gag atc cca gac cca gct tcc aga tac caa cca gag ggt gtc cac 240 Ser Glu Ile Pro Asp Pro Ala Ser Arg Tyr Gln Pro Glu Gly Val His 65 70 75 80 ggt cca tct caa atc atc caa gag tcc aag gag ttc aac aac gag acc 288 Gly Pro Ser Gln Ile Ile Gln Glu Ser Lys Glu Phe Asn Asn Glu Thr 85 90 95 ttc ttg aag aag gag gac ttg atc atc tac gag atc cac gtc ggt act 336 Phe Leu Lys Lys Glu Asp Leu Ile Ile Tyr Glu Ile His Val Gly Thr 100 105 110 ttc acc cca gag ggt act ttc gag ggt gtc atc aga aag ttg gac tac 384 Phe Thr Pro Glu Gly Thr Phe Glu Gly Val Ile Arg Lys Leu Asp Tyr 115 120 125 ttg aag gat ttg ggt atc acc gct atc gag atc atg cca atc gct caa 432 Leu Lys Asp Leu Gly Ile Thr Ala Ile Glu Ile Met Pro Ile Ala Gln 130 135 140 ttc cca ggt aag aga gac tgg ggt tac gat ggt gtt tac ttg tac gct 480 Phe Pro Gly Lys Arg Asp Trp Gly Tyr Asp Gly Val Tyr Leu Tyr Ala 145 150 155 160 gtc caa aac tcc tac ggt ggt cca gag ggt ttc aga aag ttg gtt gat 528 Val Gln Asn Ser Tyr Gly Gly Pro Glu Gly Phe Arg Lys Leu Val Asp 165 170 175 gag gct cac aag aag ggt ttg ggt gtt atc ttg gac gtt gtc tac aac 576 Glu Ala His Lys Lys Gly Leu Gly Val Ile Leu Asp Val Val Tyr Asn 180 185 190 cat gtt ggt cca gag ggt aac tac atg gtt aag ttg ggt cca tac ttc 624 His Val Gly Pro Glu Gly Asn Tyr Met Val Lys Leu Gly Pro Tyr Phe 195 200 205 agt caa aag tac aag acc cca tgg ggt ttg acc ttc aac ttc gac gac 672 Ser Gln Lys Tyr Lys Thr Pro Trp Gly Leu Thr Phe Asn Phe Asp Asp 210 215 220 gct gag tcc gat gag gtc aga aag ttc atc ttg gag aac gtt gaa tac 720 Ala Glu Ser Asp Glu Val Arg Lys Phe Ile Leu Glu Asn Val Glu Tyr 225 230 235 240 tgg atc aag gag tac aac gtt gat ggt ttc aga ttg gac gct gtc cac 768 Trp Ile Lys Glu Tyr Asn Val Asp Gly Phe Arg Leu Asp Ala Val His 245 250 255 gct atc atc gac acc tct cca aag cac atc ctc gag gag atc gct gat 816 Ala Ile Ile Asp Thr Ser Pro Lys His Ile Leu Glu Glu Ile Ala Asp 260 265 270 gtt gtc cac aag tac aac aga atc gtt atc gct gag tcc gac ttg aac 864 Val Val His Lys Tyr Asn Arg Ile Val Ile Ala Glu Ser Asp Leu Asn 275 280 285 gac cca cgt gtt gtt aac cca aag gag aag tgt ggt tac aac atc gac 912 Asp Pro Arg Val Val Asn Pro Lys Glu Lys Cys Gly Tyr Asn Ile Asp 290 295 300 gct caa tgg gtt gac gat ttc cac cac tct atc cac gct tac ttg acc 960 Ala Gln Trp Val Asp Asp Phe His His Ser Ile His Ala Tyr Leu Thr 305 310 315 320 ggt gag aga caa ggt tac tac act gac ttc ggt aac ttg gac gat atc 1008 Gly Glu Arg Gln Gly Tyr Tyr Thr Asp Phe Gly Asn Leu Asp Asp Ile 325 330 335 gtt aag tcc tac aag gac gtc ttc gtt tac gat ggt aag tac tcc aac 1056 Val Lys Ser Tyr Lys Asp Val Phe Val Tyr Asp Gly Lys Tyr Ser Asn 340 345 350 ttc aga aga aag acc cac ggt gag cca gtt ggt gag ttg gat ggt tgt 1104 Phe Arg Arg Lys Thr His Gly Glu Pro Val Gly Glu Leu Asp Gly Cys 355 360 365 aac ttc gtc gtt tac atc caa aac cac gat caa gtc ggt aac aga ggt 1152 Asn Phe Val Val Tyr Ile Gln Asn His Asp Gln Val Gly Asn Arg Gly 370 375 380 aag ggt gag aga atc att aag ctc gtc gac aga gag tcc tac aag atc 1200 Lys Gly Glu Arg Ile Ile Lys Leu Val Asp Arg Glu Ser Tyr Lys Ile 385 390 395 400 gct gct gct ttg tac ttg ttg tct cca tac atc cca atg atc ttc atg 1248 Ala Ala Ala Leu Tyr Leu Leu Ser Pro Tyr Ile Pro Met Ile Phe Met 405 410 415 ggt gag gag tac ggt gag gag aac cca ttc tac ttc ttc tct gac ttc 1296 Gly Glu Glu Tyr Gly Glu Glu Asn Pro Phe Tyr Phe Phe Ser Asp Phe 420 425 430 tcc gac tcc aag ttg atc caa ggt gtt aga gag ggt aga aag aag gag 1344 Ser Asp Ser Lys Leu Ile Gln Gly Val Arg Glu Gly Arg Lys Lys Glu 435 440 445 aac ggt caa gac act gat cca caa gac gag tcc acc ttc aac gct tcc 1392 Asn Gly Gln Asp Thr Asp Pro Gln Asp Glu Ser Thr Phe Asn Ala Ser 450 455 460 aag ttg tct tgg aag atc gat gag gag att ttc agt ttc tac aag atc 1440 Lys Leu Ser Trp Lys Ile Asp Glu Glu Ile Phe Ser Phe Tyr Lys Ile 465 470 475 480 ctt atc aag atg aga aag gag ttg tcc atc gct tgt gac aga aga gtc 1488 Leu Ile Lys Met Arg Lys Glu Leu Ser Ile Ala Cys Asp Arg Arg Val 485 490 495 aac gtt gtc aac ggt gag aac tgg ttg atc atc aag ggt aga gaa tac 1536 Asn Val Val Asn Gly Glu Asn Trp Leu Ile Ile Lys Gly Arg Glu Tyr 500 505 510 ttc tcc ttg tac gtc ttc agt aag tcc tcc atc gag gtt aag tac agt 1584 Phe Ser Leu Tyr Val Phe Ser Lys Ser Ser Ile Glu Val Lys Tyr Ser 515 520 525 ggt acc ttg ttg ttg tct tcc aac aac agt ttc cca caa cac atc gag 1632 Gly Thr Leu Leu Leu Ser Ser Asn Asn Ser Phe Pro Gln His Ile Glu 530 535 540 gag ggt aag tac gag ttc gac aag ggt ttc gct ttg tac aag ttg tag 1680 Glu Gly Lys Tyr Glu Phe Asp Lys Gly Phe Ala Leu Tyr Lys Leu 545 550 555 15 559 PRT Artificial Sequence Description of Artificial Sequence Synthetic protein 15 Met Thr Phe Ala Tyr Lys Ile Asp Gly Asn Glu Val Ile Phe Thr Leu 1 5 10 15 Trp Ala Pro Tyr Gln Lys Ser Val Lys Leu Lys Val Leu Glu Lys Gly 20 25 30 Leu Tyr Glu Met Glu Arg Asp Glu Lys Gly Tyr Phe Thr Ile Thr Leu 35 40 45 Asn Asn Val Lys Val Arg Asp Arg Tyr Lys Tyr Val Leu Asp Asp Ala 50 55 60 Ser Glu Ile Pro Asp Pro Ala Ser Arg Tyr Gln Pro Glu Gly Val His 65 70 75 80 Gly Pro Ser Gln Ile Ile Gln Glu Ser Lys Glu Phe Asn Asn Glu Thr 85 90 95 Phe Leu Lys Lys Glu Asp Leu Ile Ile Tyr Glu Ile His Val Gly Thr 100 105 110 Phe Thr Pro Glu Gly Thr Phe Glu Gly Val Ile Arg Lys Leu Asp Tyr 115 120 125 Leu Lys Asp Leu Gly Ile Thr Ala Ile Glu Ile Met Pro Ile Ala Gln 130 135 140 Phe Pro Gly Lys Arg Asp Trp Gly Tyr Asp Gly Val Tyr Leu Tyr Ala 145 150 155 160 Val Gln Asn Ser Tyr Gly Gly Pro Glu Gly Phe Arg Lys Leu Val Asp 165 170 175 Glu Ala His Lys Lys Gly Leu Gly Val Ile Leu Asp Val Val Tyr Asn 180 185 190 His Val Gly Pro Glu Gly Asn Tyr Met Val Lys Leu Gly Pro Tyr Phe 195 200 205 Ser Gln Lys Tyr Lys Thr Pro Trp Gly Leu Thr Phe Asn Phe Asp Asp 210 215 220 Ala Glu Ser Asp Glu Val Arg Lys Phe Ile Leu Glu Asn Val Glu Tyr 225 230 235 240 Trp Ile Lys Glu Tyr Asn Val Asp Gly Phe Arg Leu Asp Ala Val His 245 250 255 Ala Ile Ile Asp Thr Ser Pro Lys His Ile Leu Glu Glu Ile Ala Asp 260 265 270 Val Val His Lys Tyr Asn Arg Ile Val Ile Ala Glu Ser Asp Leu Asn 275 280 285 Asp Pro Arg Val Val Asn Pro Lys Glu Lys Cys Gly Tyr Asn Ile Asp 290 295 300 Ala Gln Trp Val Asp Asp Phe His His Ser Ile His Ala Tyr Leu Thr 305 310 315 320 Gly Glu Arg Gln Gly Tyr Tyr Thr Asp Phe Gly Asn Leu Asp Asp Ile 325 330 335 Val Lys Ser Tyr Lys Asp Val Phe Val Tyr Asp Gly Lys Tyr Ser Asn 340 345 350 Phe Arg Arg Lys Thr His Gly Glu Pro Val Gly Glu Leu Asp Gly Cys 355 360 365 Asn Phe Val Val Tyr Ile Gln Asn His Asp Gln Val Gly Asn Arg Gly 370 375 380 Lys Gly Glu Arg Ile Ile Lys Leu Val Asp Arg Glu Ser Tyr Lys Ile 385 390 395 400 Ala Ala Ala Leu Tyr Leu Leu Ser Pro Tyr Ile Pro Met Ile Phe Met 405 410 415 Gly Glu Glu Tyr Gly Glu Glu Asn Pro Phe Tyr Phe Phe Ser Asp Phe 420 425 430 Ser Asp Ser Lys Leu Ile Gln Gly Val Arg Glu Gly Arg Lys Lys Glu 435 440 445 Asn Gly Gln Asp Thr Asp Pro Gln Asp Glu Ser Thr Phe Asn Ala Ser 450 455 460 Lys Leu Ser Trp Lys Ile Asp Glu Glu Ile Phe Ser Phe Tyr Lys Ile 465 470 475 480 Leu Ile Lys Met Arg Lys Glu Leu Ser Ile Ala Cys Asp Arg Arg Val 485 490 495 Asn Val Val Asn Gly Glu Asn Trp Leu Ile Ile Lys Gly Arg Glu Tyr 500 505 510 Phe Ser Leu Tyr Val Phe Ser Lys Ser Ser Ile Glu Val Lys Tyr Ser 515 520 525 Gly Thr Leu Leu Leu Ser Ser Asn Asn Ser Phe Pro Gln His Ile Glu 530 535 540 Glu Gly Lys Tyr Glu Phe Asp Lys Gly Phe Ala Leu Tyr Lys Leu 545 550 555 16 15 DNA Artificial Sequence Description of Artificial Sequence Sequence which is common to intron 16 gtatgttact aacag 15 17 23 DNA Artificial Sequence Description of Artificial Sequence Synthetic DNA 17 tgtggaaaac ttgcttggtt tga 23 18 10 DNA Artificial Sequence Description of Artificial Sequence Primer 18 agcggccgct 10 19 30 DNA Artificial Sequence Description of Artificial Sequence Primer 19 cctgcaggaa acgtaaacaa agaggtttca 30 20 30 DNA Artificial Sequence Description of Artificial Sequence Primer 20 cctgcaggcc cacgcaacac ctggtgtctg 30 21 30 DNA Artificial Sequence Description of Artificial Sequence Primer 21 ggtcgactcg cttttgtgcg tgtgtgcatt 30 22 30 DNA Artificial Sequence Description of Artificial Sequence Primer 22 gggtcgacat gtcaccacgt tatcgtacac 30 23 25 DNA Artificial Sequence Description of Artificial Sequence Primer 23 ggagatctgc ccattgcgca atctt 25 24 26 DNA Artificial Sequence Description of Artificial Sequence Primer 24 ggagatctca ccaacgccca cggtgt 26 25 30 DNA Artificial Sequence Description of Artificial Sequence Primer 25 ggggtaccta gccaccactg acaacctcat 30 26 27 DNA Artificial Sequence Description of Artificial Sequence Primer 26 cctgcagacc ggtgaaattt atcgaaa 27 27 30 DNA Artificial Sequence Description of Artificial Sequence Primer 27 gagatctgat gatgcctgtt gatattcatc 30 28 26 DNA Artificial Sequence Description of Artificial Sequence Primer 28 gagatctcta caatggctcg ttccca 26 29 36 DNA Artificial Sequence Description of Artificial Sequence Primer 29 cctgcagggc ggccgctttt gtgcgtgtgt gcattt 36 30 38 DNA Artificial Sequence Description of Artificial Sequence Primer 30 agcggccgct agcttacagc gagcactcaa atctgccc 38 31 41 DNA Artificial Sequence Description of Artificial Sequence Primer 31 gggatcctct agatatgttg tttgtaagtg tgttttgtat c 41 32 30 DNA Artificial Sequence Description of Artificial Sequence Primer 32 ggggatccat tgtatgactt ttatttatgg 30 33 28 DNA Artificial Sequence Description of Artificial Sequence Primer 33 ccctgcaggg ataaagctga agaataat 28 34 2330 DNA Candida utilis 34 aagcttatgg aggagattgg gaagattgaa cgaggtgaga tggacacgtt gctgattgac 60 gagatcggca agaaggaggc acctgtggtg aaaccactta cacccgacgt ggatagtaat 120 gtaacagggg aaccgactgg acatagttct acgacaccac caccggtgga acaggactcg 180 agcacaacca cgaggaagag agcacaagac gatggtgagg aaaacacaag gaagaagccc 240 aaggttgagg cagagaaaaa ggcagagcaa gaggcagaga aagaggcaga gaaagaggca 300 gagaaagagg cagagcaaga ggcagagaaa gaggctccgc gtgcagtgcc gaacaagaga 360 ctacaacaca ttgctactcc tctcatcgag agcatctcgt catacaagta cgcctcagcg 420 tttctacacc ctgttaacga gtccagtgca cccaactatt actctctgat caagaaacca 480 agggatctga agaccatcaa acagatggtc aaggacggac gtatacagac caatcttgag 540 ctggagaggg agatcttgct gatgtttgcc aatgccatca tgtacaacaa gaccgggacg 600 gatatctacg agtggaccaa ggagatgcag ccggaagttg acaagctcat cgagctgttt 660 aacgagagta aataggatac aggctagaga tcaaaagaag aatagaaaca gctcgataaa 720 acggtattgt aagtggtatg tacaaagggg tgtgtcttgc tcaacgtctt tgcatctgct 780 gagtcaaagc agcgttctgc tcttggaatc taagaccgac tctttccgaa tgcttgagga 840 acttttcaga gcacttcaac acacaggatt cctcctttga tgatagcttt tcagaggtga 900 agtcgttgac acagtcgctg aaacaacgct caacgaggtt ggaataaaga cgcataaagt 960 ccttcatctg cttctgctca acaagctgct ggaactgctg ctgctctttt gggttcaatt 1020 ggtccatcct tgctactttt ccgcctagtt tcgattccga ttctgataga gaagcccagc 1080 tatgaatgga agaaattttt cacttttgta tgtccttttt ttcacgcttc gttgcttcgg 1140 acaaaaaaat agtggaggca ctcggtggag ggaagctatc ctcgagatga aaaatttcaa 1200 gctcatctca tcgtccaagt gggacagcaa gctgaggctt ctgaagaggt tgaggaaaat 1260 ggtcaccacg ttatcgtaca cagagagggc atcgcagcac ccttcgccac ttgctaagcg 1320 tctgttttcg cttatggagt ccaagaagac gaacctgtgt gccagtgtcg atgttcgtac 1380 cacagaggag ttgctcaagc tcgttgatac gcttggtcct tatatctgtc tgttgaagac 1440 gcatattgat atcattgatg acttctctat ggagtctact gtggctccac tgttggagct 1500 ttcaaagaag cacaatttcc tcatctttga ggaccgtaag tttgctgata tcggcaacac 1560 cgtcaaggca cagtacgccg gtggtgcgtt caagattgcg caatgggcag atatcaccaa 1620 cgcccacggt gtcaccggtg caggtatcgt caaggggttg aaggaggctg cacaggaaac 1680 cacggatgag ccaagagggc tgttgatgct tgcggagctg agctccaagg gctccttggc 1740 ccacgggaca tataccgagg agaccgtgga gattgccaaa actgataagg acttttgtat 1800 tggattcatc gcacagagag acatgggtgg cagagaagat gggttcgact ggatcatcat 1860 gacaccaggc gtgggactcg acgataaggg cgactccctg ggccaacagt acagaactgt 1920 cgatgaggtt gtcagtggtg gctctgacat catcatcgtt ggtagaggct tgtttggaaa 1980 gggaagagat ccaacagtgg aaggtgagcg ttatagaaaa gcaggctggg atgcttatct 2040 caagagatgc tcagctcaat aagcgttgag ctctggcttg tataggttca cttgtataaa 2100 atgttcatta ctgttttcgg aagttgtaga ttgccatttt tgcgcaaatt gacgccagtc 2160 tttttttgcg ccaaatgtca gtttttttgc gccaaaattt acttcatctt atacaactgc 2220 aaaaaccatc caatccaatc cagaaaggac tgatcaatgg tggtgattga ctcaagttct 2280 gatgctacac aacagacaga gctctctaaa aagaattcga tatcaagctt 2330 35 804 DNA Candida utilis CDS (1)..(801) 35 atg gtc acc acg tta tcg tac aca gag agg gca tcg cag cac cct tcg 48 Met Val Thr Thr Leu Ser Tyr Thr Glu Arg Ala Ser Gln His Pro Ser 1 5 10 15 cca ctt gct aag cgt ctg ttt tcg ctt atg gag tcc aag aag acg aac 96 Pro Leu Ala Lys Arg Leu Phe Ser Leu Met Glu Ser Lys Lys Thr Asn 20 25 30 ctg tgt gcc agt gtc gat gtt cgt acc aca gag gag ttg ctc aag ctc 144 Leu Cys Ala Ser Val Asp Val Arg Thr Thr Glu Glu Leu Leu Lys Leu 35 40 45 gtt gat acg ctt ggt cct tat atc tgt ctg ttg aag acg cat att gat 192 Val Asp Thr Leu Gly Pro Tyr Ile Cys Leu Leu Lys Thr His Ile Asp 50 55 60 atc att gat gac ttc tct atg gag tct act gtg gct cca ctg ttg gag 240 Ile Ile Asp Asp Phe Ser Met Glu Ser Thr Val Ala Pro Leu Leu Glu 65 70 75 80 ctt tca aag aag cac aat ttc ctc atc ttt gag gac cgt aag ttt gct 288 Leu Ser Lys Lys His Asn Phe Leu Ile Phe Glu Asp Arg Lys Phe Ala 85 90 95 gat atc ggc aac acc gtc aag gca cag tac gcc ggt ggt gcg ttc aag 336 Asp Ile Gly Asn Thr Val Lys Ala Gln Tyr Ala Gly Gly Ala Phe Lys 100 105 110 att gcg caa tgg gca gat atc acc aac gcc cac ggt gtc acc ggt gca 384 Ile Ala Gln Trp Ala Asp Ile Thr Asn Ala His Gly Val Thr Gly Ala 115 120 125 ggt atc gtc aag ggg ttg aag gag gct gca cag gaa acc acg gat gag 432 Gly Ile Val Lys Gly Leu Lys Glu Ala Ala Gln Glu Thr Thr Asp Glu 130 135 140 cca aga ggg ctg ttg atg ctt gcg gag ctg agc tcc aag ggc tcc ttg 480 Pro Arg Gly Leu Leu Met Leu Ala Glu Leu Ser Ser Lys Gly Ser Leu 145 150 155 160 gcc cac ggg aca tat acc gag gag acc gtg gag att gcc aaa act gat 528 Ala His Gly Thr Tyr Thr Glu Glu Thr Val Glu Ile Ala Lys Thr Asp 165 170 175 aag gac ttt tgt att gga ttc atc gca cag aga gac atg ggt ggc aga 576 Lys Asp Phe Cys Ile Gly Phe Ile Ala Gln Arg Asp Met Gly Gly Arg 180 185 190 gaa gat ggg ttc gac tgg atc atc atg aca cca ggc gtg gga ctc gac 624 Glu Asp Gly Phe Asp Trp Ile Ile Met Thr Pro Gly Val Gly Leu Asp 195 200 205 gat aag ggc gac tcc ctg ggc caa cag tac aga act gtc gat gag gtt 672 Asp Lys Gly Asp Ser Leu Gly Gln Gln Tyr Arg Thr Val Asp Glu Val 210 215 220 gtc agt ggt ggc tct gac atc atc atc gtt ggt aga ggc ttg ttt gga 720 Val Ser Gly Gly Ser Asp Ile Ile Ile Val Gly Arg Gly Leu Phe Gly 225 230 235 240 aag gga aga gat cca aca gtg gaa ggt gag cgt tat aga aaa gca ggc 768 Lys Gly Arg Asp Pro Thr Val Glu Gly Glu Arg Tyr Arg Lys Ala Gly 245 250 255 tgg gat gct tat ctc aag aga tgc tca gct caa taa 804 Trp Asp Ala Tyr Leu Lys Arg Cys Ser Ala Gln 260 265 36 267 PRT Candida utilis 36 Met Val Thr Thr Leu Ser Tyr Thr Glu Arg Ala Ser Gln His Pro Ser 1 5 10 15 Pro Leu Ala Lys Arg Leu Phe Ser Leu Met Glu Ser Lys Lys Thr Asn 20 25 30 Leu Cys Ala Ser Val Asp Val Arg Thr Thr Glu Glu Leu Leu Lys Leu 35 40 45 Val Asp Thr Leu Gly Pro Tyr Ile Cys Leu Leu Lys Thr His Ile Asp 50 55 60 Ile Ile Asp Asp Phe Ser Met Glu Ser Thr Val Ala Pro Leu Leu Glu 65 70 75 80 Leu Ser Lys Lys His Asn Phe Leu Ile Phe Glu Asp Arg Lys Phe Ala 85 90 95 Asp Ile Gly Asn Thr Val Lys Ala Gln Tyr Ala Gly Gly Ala Phe Lys 100 105 110 Ile Ala Gln Trp Ala Asp Ile Thr Asn Ala His Gly Val Thr Gly Ala 115 120 125 Gly Ile Val Lys Gly Leu Lys Glu Ala Ala Gln Glu Thr Thr Asp Glu 130 135 140 Pro Arg Gly Leu Leu Met Leu Ala Glu Leu Ser Ser Lys Gly Ser Leu 145 150 155 160 Ala His Gly Thr Tyr Thr Glu Glu Thr Val Glu Ile Ala Lys Thr Asp 165 170 175 Lys Asp Phe Cys Ile Gly Phe Ile Ala Gln Arg Asp Met Gly Gly Arg 180 185 190 Glu Asp Gly Phe Asp Trp Ile Ile Met Thr Pro Gly Val Gly Leu Asp 195 200 205 Asp Lys Gly Asp Ser Leu Gly Gln Gln Tyr Arg Thr Val Asp Glu Val 210 215 220 Val Ser Gly Gly Ser Asp Ile Ile Ile Val Gly Arg Gly Leu Phe Gly 225 230 235 240 Lys Gly Arg Asp Pro Thr Val Glu Gly Glu Arg Tyr Arg Lys Ala Gly 245 250 255 Trp Asp Ala Tyr Leu Lys Arg Cys Ser Ala Gln 260 265 37 2086 DNA Candida utilis 37 ggatccaatc gttgaaagtg atcaagctga ttacaaaagt aagtatgaaa agagccaatg 60 ttgagagtct caggaaccac atcgacttct tcgtgccatc ctcccacatt ctgaagccca 120 agaacccaca aatcatcaaa caccaacacg atgcggacgc caacccgagt tgtaacgcca 180 caaagtacgg gtacgaccct gttccaggag ggctcacgcc gcaatcaaca accaaagtcg 240 ccacgatcaa cgccagtatc aagtaaaaga agaatagcat ctccagtctt ccgatagctg 300 tgtacttcga tctgacgttg tagatgatga tgatcatgat cacgagggca ccaatgttga 360 caaaggcgtt accaatctgg aatatcacgg tattggcaac gtctatcgga cgggcgtagc 420 actcagggat gatcccttcg ttcaggtgcg tgaactgctc gttcgtcgtt gccttcacaa 480 cctggcacaa cgggagcggc gtgttgtggc atagcgagtt gaaatcaccg aatgccattg 540 tgttttatcg ttagggagac ctgtttgaag ctgacagcgg gatgaagatg aggaaggaga 600 gcacaacagc tgagcggaag tctctgtgat gcttggtgga ccgggtgtag gtggaatctc 660 cctggtgagc gtacttgcaa cggtgctcag cgacttcttc tcgagaggaa acgtaaacaa 720 agaggtttca atgttgatgt tgatgtgtat ttttgttaca aaagcagaaa ttgtaaacaa 780 aaaggtataa ttagggctct ggtgtaatga tgggcacgtg acgttaccgt gctggtcgat 840 tttagggcta ttggttcgcg tcccgctggt gtccgggtta gcgtgtcaat gtggcgcctc 900 ccgattatta cataagaaaa cacccaccca cgcaacacct ggtgtctgga tgttgacgct 960 ttgtatgcgt gtgtgtgttt tttcttccgt cttgttgggc cactctgcgc gagcgttggc 1020 gactcaccgg tgaaatttat cgaaaacttt caggctcagg cccttttcaa cactaccctt 1080 tgagatcaca tcaagcagta atcaaacaca atgggtatgt gggaaacgac gacgtgtgcg 1140 gtgtgtgaat gccattagtg ggatatgtgg tagtctcgag cgtggatatt atcgataggg 1200 atggtgcttg ttctatacgt cttgctggga aggaagaaag cgatgaagta tgtgggaaga 1260 aggggtggtt taagagagga agtagacatg taacaagtgt gttcagagaa caaggacgga 1320 aatatcacct atatgacgta cacatcacga actgctcctg gaggaagcga caagatgaat 1380 atcaacaggc atcatcatat ctctacaatg gctcgttccc aaagcacacg cacaaacaaa 1440 tccgagactt ttgtactaac agctgtatct ctgacaaata gttaacgttc caaagaccag 1500 aagaacctac tgtaagggta aggagtgcag aaagcacact caacacaagg ttacccagta 1560 caaggctggt aaggcttccc tctttgccca gggtaagcgt cgttatgacc gtaagcaatc 1620 cggttacggt ggtcaaacca agccagtttt ccacaaaaag gctaaaacca ccaagaaggt 1680 tgttttgcgt ttggagtgtg ttgtctgcaa gaccaaggcc caattggctt tgaagcgttg 1740 taagcacttc gagttgggtg gtgacaagaa gcaaaagggt caagctttgc aattctaagc 1800 ttaagacaat tgttgaaagt tttattatta tcactacact gtgtttttga tgtcatctaa 1860 tgtaaaagcg tttatattac cacttggttc ggtatcctgt agaagaatac ggcctgtagc 1920 gtagcattcc cacaggagga tcacagcaac atagaccaaa caatgtcacg cacggggatc 1980 gaacgcggaa ccaaacctct ccctcctccc cctttcaccg cggttatttt gttatgggca 2040 cacacagggg aaggaaaaaa atgcacacac gcacaaaagc gagctc 2086 38 688 DNA Candida utilis CDS join(1..4, 372..685) 38 atg g gtatgtggga aacgacgacg tgtgcggtgt gtgaatgcca ttagtgggat 54 Met 1 atgtggtagt ctcgagcgtg gatattatcg atagggatgg tgcttgttct atacgtcttg 114 ctgggaagga agaaagcgat gaagtatgtg ggaagaaggg gtggtttaag agaggaagta 174 gacatgtaac aagtgtgttc agagaacaag gacggaaata tcacctatat gacgtacaca 234 tcacgaactg ctcctggagg aagcgacaag atgaatatca acaggcatca tcatatctct 294 acaatggctc gttcccaaag cacacgcaca aacaaatccg agacttttgt actaacagct 354 gtatctctga caaatag tt aac gtt cca aag acc aga aga acc tac tgt 403 Val Asn Val Pro Lys Thr Arg Arg Thr Tyr Cys 5 10 aag ggt aag gag tgc aga aag cac act caa cac aag gtt acc cag tac 451 Lys Gly Lys Glu Cys Arg Lys His Thr Gln His Lys Val Thr Gln Tyr 15 20 25 aag gct ggt aag gct tcc ctc ttt gcc cag ggt aag cgt cgt tat gac 499 Lys Ala Gly Lys Ala Ser Leu Phe Ala Gln Gly Lys Arg Arg Tyr Asp 30 35 40 cgt aag caa tcc ggt tac ggt ggt caa acc aag cca gtt ttc cac aaa 547 Arg Lys Gln Ser Gly Tyr Gly Gly Gln Thr Lys Pro Val Phe His Lys 45 50 55 60 aag gct aaa acc acc aag aag gtt gtt ttg cgt ttg gag tgt gtt gtc 595 Lys Ala Lys Thr Thr Lys Lys Val Val Leu Arg Leu Glu Cys Val Val 65 70 75 39 106 PRT Candida utilis 39 Met Val Asn Val Pro Lys Thr Arg Arg Thr Tyr Cys Lys Gly Lys Glu 1 5 10 15 Cys Arg Lys His Thr Gln His Lys Val Thr Gln Tyr Lys Ala Gly Lys 20 25 30 Ala Ser Leu Phe Ala Gln Gly Lys Arg Arg Tyr Asp Arg Lys Gln Ser 35 40 45 Gly Tyr Gly Gly Gln Thr Lys Pro Val Phe His Lys Lys Ala Lys Thr 50 55 60 Thr Lys Lys Val Val Leu Arg Leu Glu Cys Val Val Cys Lys Thr Lys 65 70 75 80 Ala Gln Leu Ala Leu Lys Arg Cys Lys His Phe Glu Leu Gly Gly Asp 85 90 95 Lys Lys Gln Lys Gly Gln Ala Leu Gln Phe 100 105 40 1113 DNA Candida utilis 40 ggatccaatc gttgaaagtg atcaagctga ttacaaaagt aagtatgaaa agagccaatg 60 ttgagagtct caggaaccac atcgacttct tcgtgccatc ctcccacatt ctgaagccca 120 agaacccaca aatcatcaaa caccaacacg atgcggacgc caacccgagt tgtaacgcca 180 caaagtacgg gtacgaccct gttccaggag ggctcacgcc gcaatcaaca accaaagtcg 240 ccacgatcaa cgccagtatc aagtaaaaga agaatagcat ctccagtctt ccgatagctg 300 tgtacttcga tctgacgttg tagatgatga tgatcatgat cacgagggca ccaatgttga 360 caaaggcgtt accaatctgg aatatcacgg tattggcaac gtctatcgga cgggcgtagc 420 actcagggat gatcccttcg ttcaggtgcg tgaactgctc gttcgtcgtt gccttcacaa 480 cctggcacaa cgggagcggc gtgttgtggc atagcgagtt gaaatcaccg aatgccattg 540 tgttttatcg ttagggagac ctgtttgaag ctgacagcgg gatgaagatg aggaaggaga 600 gcacaacagc tgagcggaag tctctgtgat gcttggtgga ccgggtgtag gtggaatctc 660 cctggtgagc gtacttgcaa cggtgctcag cgacttcttc tcgagaggaa acgtaaacaa 720 agaggtttca atgttgatgt tgatgtgtat ttttgttaca aaagcagaaa ttgtaaacaa 780 aaaggtataa ttagggctct ggtgtaatga tgggcacgtg acgttaccgt gctggtcgat 840 tttagggcta ttggttcgcg tcccgctggt gtccgggtta gcgtgtcaat gtggcgcctc 900 ccgattatta cataagaaaa cacccaccca cgcaacacct ggtgtctgga tgttgacgct 960 ttgtatgcgt gtgtgtgttt tttcttccgt cttgttgggc cactctgcgc gagcgttggc 1020 gactcaccgg tgaaatttat cgaaaacttt caggctcagg cccttttcaa cactaccctt 1080 tgagatcaca tcaagcagta atcaaacaca atg 1113 41 90 DNA Artificial Sequence Description of Artificial Sequence Primer 41 ggtctagata tgaccttcgc ttacaagatc gatggtaacg aggttatctt cactttgtgg 60 gctccatacc aaaagtccgt taagttgaag 90 42 89 DNA Artificial Sequence Description of Artificial Sequence Primer 42 ataccaaaag tccgttaagt tgaaggtctt ggagaagggt ttgtacgaga tggagagaga 60 cgagaagggt tacttcacca tcactttga 89 43 90 DNA Artificial Sequence Description of Artificial Sequence Primer 43 ggccttggac tcttggatga tttgagatgg accgtggaca ccctctggtt ggtatctgga 60 agctgggtct gggatctcgg aagcatcgtc 90 44 87 DNA Artificial Sequence Description of Artificial Sequence Primer 44 ggtctgggat ctcggaagca tcgtccaaaa cgtacttgta tctgtctctg accttgacgt 60 tgttcaaagt gatggtgaag taaccct 87 45 100 DNA Artificial Sequence Description of Artificial Sequence Primer 45 aaccaaggag ttcaacaacg agaccttctt gaagaaggag gacttgatca tctacgagat 60 ccacgtcggt actttcaccc cagagggtac tttcgagggt 100 46 100 DNA Artificial Sequence Description of Artificial Sequence Primer 46 ccccagaggg tactttcgag ggtgtcatca gaaagttgga ctacttgaag gatttgggta 60 tcaccgctat cgagatcatg ccaatcgctc aattcccagg 100 47 100 DNA Artificial Sequence Description of Artificial Sequence Primer 47 aagtagacaa cgtccaagat aacacccaaa cccttcttgt gagcctcatc aaccaacttt 60 ctgaaaccct ctggaccacc gtaggagttt tggacagcgt 100 48 100 DNA Artificial Sequence Description of Artificial Sequence Primer 48 accgtaggag ttttggacag cgtacaagta aacaccatcg taaccccagt ctctcttacc 60 tgggaattga gcgattggca tgatctcgat agcggtgata 100 49 74 DNA Artificial Sequence Description of Artificial Sequence Primer 49 atgtctacaa ccatgttggt ccagagggta actacatggt taagttgggt ccatacttca 60 gtcaaaagta caag 74 50 80 DNA Artificial Sequence Description of Artificial Sequence Primer 50 catacttcag tcaaaagtac aagaccccat ggggtttgac cttcaacttc gacgacgctg 60 agtccgatga ggtcagaaag 80 51 75 DNA Artificial Sequence Description of Artificial Sequence Primer 51 agctcgagga tgtgctttgg agaggtgtcg atgatagcgt ggacagcgtc caatctgaaa 60 ccatcaacgt tgtac 75 52 73 DNA Artificial Sequence Description of Artificial Sequence Primer 52 aaccatcaac gttgtactcc ttgatccagt attcaacgtt ctccaagatg aactttctga 60 cctcatcgga ctc 73 53 69 DNA Artificial Sequence Description of Artificial Sequence Primer 53 tcctcgagga gatcgctgat gttgtccaca agtacaacag aatcgttatc gctgagtccg 60 acttgaacg 69 54 68 DNA Artificial Sequence Description of Artificial Sequence Primer 54 gctgagtccg acttgaacga cccacgtgtt gttaacccaa aggagaagtg tggttacaac 60 atcgacgc 68 55 69 DNA Artificial Sequence Description of Artificial Sequence Primer 55 tggatatcgt ccaagttacc gaagtcagtg tagtaacctt gtctctcacc ggtcaagtaa 60 gcgtggata 69 56 67 DNA Artificial Sequence Description of Artificial Sequence Primer 56 ggtcaagtaa gcgtggatag agtggtggaa atcgtcaacc cattgagcgt cgatgttgta 60 accacac 67 57 100 DNA Artificial Sequence Description of Artificial Sequence Primer 57 cagatatcgt taagtcctac aaggacgtct tcgtttacga tggtaagtac tccaacttca 60 gaagaaagac ccacggtgag ccagttggtg agttggatgg 100 58 100 DNA Artificial Sequence Description of Artificial Sequence Primer 58 aagtcgacga gcttaatgat tctctcaccc ttacctctgt taccgacttg atcgtggttt 60 tggatgtaaa cgacgaagtt acaaccatcc aactcaccaa 100 59 76 DNA Artificial Sequence Description of Artificial Sequence Primer 59 tcgtcgacag agagtcctac aagatcgctg ctgctttgta cttgttgtct ccatacatcc 60 caatgatctt catggg 76 60 76 DNA Artificial Sequence Description of Artificial Sequence Primer 60 catcccaatg atcttcatgg gtgaggagta cggtgaggag aacccattct acttcttctc 60 tgacttctcc gactcc 76 61 75 DNA Artificial Sequence Description of Artificial Sequence Primer 61 tcatcgatct tccaagacaa cttggaagcg ttgaaggtgg actcgtcttg tggatcagtg 60 tcttgaccgt tctcc 75 62 77 DNA Artificial Sequence Description of Artificial Sequence Primer 62 cagtgtcttg accgttctcc ttctttctac cctctctaac accttggatc aacttggagt 60 cggagaagtc agagaag 77 63 82 DNA Artificial Sequence Description of Artificial Sequence Primer 63 agatcgatga ggagattttc agtttctaca agatccttat caagatgaga aaggagttgt 60 ccatcgcttg tgacagaaga gt 82 64 91 DNA Artificial Sequence Description of Artificial Sequence Primer 64 ccatcgcttg tgacagaaga gtcaacgttg tcaacggtga gaactggttg atcatcaagg 60 gtagagaata cttctccttg tacgtcttca g 91 65 80 DNA Artificial Sequence Description of Artificial Sequence Primer 65 cgagatctgc tacaacttgt acaaagcgaa acccttgtcg aactcgtact taccctcctc 60 gatgtgttgt gggaaactgt 80 66 92 DNA Artificial Sequence Description of Artificial Sequence Primer 66 cgatgtgttg tgggaaactg ttgttggaag acaacaacaa ggtaccactg tacttaacct 60 cgatggagga cttactgaag acgtacaagg ag 92 

What is claimed is:
 1. A vector comprising a marker gene for selecting transformants, a shortened promoter sequence that is operably linked to the marker gene, and a homologous DNA sequence that is homologous to chromosomal DNA, other than an rDNA sequence, of Candid utilis, and optionally a heterologous gene or gene isolated from C. utilis, wherein the vector is linearized by cleaving within or at both ends of the homologous DNA sequence with a restriction enzyme, wherein the heterologous gene or gene isolated from Candida utilis can be integrated into the chromosomal DNA of Candida utilis by homologous recombination, and wherein the shortened promoter is a promoter truncated at its 5′ terminus to decrease, relative to pCLRE11, the transformation frequency of the vector in host cells of Candida utilis and to increase, relative to pCLRE11, copy number of the vector in host cells of Candida utilis.
 2. A vector of claim 1 wherein the marker gene, the shortened promoter sequence, and the heterologous gene or the gene isolated from Candida utilis is flanked at both ends by the homologous DNA sequence.
 3. A vector of claim 1 wherein the shortened promoter sequence is isolated from Candida utilis.
 4. A vector of claim 1 wherein the shortened promoter sequence is isolated from the L41 gene of Candida utilis, the phosphoglyceric acid kinase (GAP) gene, or a plasma membrane proton ATPase (PMA) gene.
 5. A vector of claim 1 wherein the shortened promoter sequence is isolated from the L41 gene of Candida utilis.
 6. A vector of claim 5 wherein the shortened promoter sequence is a sequence which comprises the DNA sequence of nucleotides X-192 of SEQ ID NO:1, wherein X represents an integer 1 to
 111. 7. A vector of claim 5 wherein the shortened promoter sequence is a sequence selected from the group consisting of SEQ ID NO:1, SEQ ID NO:2, and SEQ ID NO:3.
 8. A vector of claim 1 wherein the homologous DNA sequence is a gene sequence isolated from Candida utilis or a partial DNA sequence thereof.
 9. A vector of claim 8 wherein the homologous DNA sequence is selected from the group consisting of a URA3A gene sequence, a L41 gene sequence, a PGK gene sequence, a GAP gene sequence, a PMA gene sequence and partial DNA sequences thereof.
 10. A vector of claim 9 wherein the homologous DNA sequence is the URA3 gene sequence or a partial DNA sequence thereof.
 11. A vector of claim 1 wherein the marker gene is a drug-resistance marker gene.
 12. A vector of claim 11 wherein the drug-resistance marker gene is a gene conferring cycloheximide resistance.
 13. A vector of claim 12 wherein the gene conferring cycloheximide resistance is a modified cycloheximide-resistance L41 gene.
 14. A vector of claim 1 wherein the heterologous gene is a gene coding for a protein or a peptide selected from the group consisting of a single-chain monellin, glycosylation inhibiting factor (GIF), serum albumin, α- or β-globulin, factor VIII, factor IX, fibronectin, α-1-antitrypsin, interleukin, interferon, G-CSF, GM-CSF, PDGF, EGF, FGF, erythropoietin, thrombopoietin, insulin, antigen polypeptides isolated from viruses for vaccine production, proteins having immune suppression activity, chymosin, amylase, lipase, cellulase, protease and pectinase.
 15. A vector of claim 1 wherein the heterologous gene is a single-chain monellin gene.
 16. A vector of claim 15 wherein the single chain monellin gene comprises a DNA sequence coding for the amino acid sequence of SEQ ID NO. 5 or the amino acid sequence of SEQ ID NO.
 6. 